This is an interesting idea in this thread. I hope that I can make time to go back and read through.
This makes me wonder about the potential for a sump with a dedicated DSB area to use with freshwater systems having high bioload.
Here are my posts from this thread in a nutshell I've edited but there are still redundancies, errors, and omissions-please forgive:
How Freshwater Deep Sand Beds Work
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These postings are my theories on how my particular FWDSB tank works and the principles by which others should be able to work. I use a bunch of facts but a lot is either just from trial, experience, and observation or my theories about what I've observed, and my best guesses.
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Many variants of the FWDSB will work, so long as they're based on certain underlying principles. Operating within those principles, all kinds of FWDSBs can be set up that get the job done.
Diffusion of nutrients, toxins, and gases through the sand: this requires the sand to be open. For the sand to be loose and open, it must be fairly large grained and/or opened up and turned over by organisms.*
Bacterial populations requiring different levels of oxygen from fully oxygenated to anoxic must not be disrupted too much: for the bacteria to do their metabolic jobs converting and freeing nutrients as well as neutralizing toxins, they must have stable environments with consistent oxygen levels or lack of oxygen.
The organisms of the FWDSB, both microbes and multicellular, exist in a balance like a mini-ecosystem: Each organism has some effect on the others, whether it be the animals which make mulm being responsible for feeding the DSB, the aerobic bacteria for destroying H2S, plants for introducing oxygen deep enough for the aerobic bacteria to metabolize poisons down deep, or animals turning over the sand to help oxygenate it deeper.
Why FWDSBs?*
What FWDSBs can accomplish include high capacity biofiltration of ammonia to NO2 to NO3, denitrification, providing a fertile substrate for rich plant growth, boosting dissolved CO2, diminished need for water changes, elimination of vacuuming, and neutralization of toxins such as H2S which accumulate beneath sand beds.
The sand bed in my tank is three inches deep, and has planaria, california blackworms, and malaysian trumpet snails for critters and it's planted with plenty of roots, extending usually 1.5 to 2 inches in depth.
My tank water never goes above 10ppm NO3 even though I almost never do water changes. Also, the NH3/NH4 and NO2 levels are consistently zero. All this despite the woefully inadequate filter I chose to replace the B9's stock filter with.
My experience with FWDSBs is that: They are not hazardous to fish and invert life, they control nitrates, mulm disintegrates to the point where it sifts into the sand to provide nutrients for many burrowing invertebrates and rooted aquatic plants, that even plants requiring rich planting media will thrive once the sand/mulm layer is established, the sand beds do not require stirring or vacuuming, that cories and kuhli loaches love DSBs, and that the water in FWDSB tanks is consistently of good quality.
I know not everyone's experience agrees with mine and I believe that is because of the differences between our particular FWDSBs. My theory is that my DSB works the way it does is because of the invertebrates and rooted plants support the principle of diffusion within the sand and the principle of not disturbing bacteria communities but actually maintain and create a stable environment which extends deeper into the sand than it would without them. Their interrelationships work out this way because they act as an ecosystem; each organism does a service which supports the functioning of another organism. Also, my DSB works because the sand is coarse with rounded grains and doesn't pack down very much at all, which supports the activity of the organisms and the diffusion of nutrients, gasses, and toxins.
Though my tank is not a Walstad tank, it is inspired and informed by her method and information as presented in "Ecology of the Planted Aquarium." I suggest that book as a great source of information about nutrients, bacteria, lighting, etc., comprehensible to the layperson
Who does what in my deep sand bed?
1. What is in the sand bed?
Sand: First of all, there is the sand. Sand is essential to have a sand bed.*Also, the nature of the sand you use will greatly effect how your sand bed performs. I recommend the kind of sand I use, which is a quartz based, fairly smooth grained (as opposed so sharp grained sand - which will hurt your cories btw) sand. What I get is a river sand that the guy at my LFS pre-washes and repackages so I haven't figured where to procure the stuff on the cheap.
There are four primary organisms aside from the protozoans, bacteria, and microfungi which live on/in the sand of a complete FWDSB:
Rooted plants
California blackworms
Planaria
Malaysian trumpet snails
In addition, some other organisms contribute but I don't think they're needed:
Tiger shrimp
Kuhli loaches
Scuds
Pond snails
And last but not least, an essential non-organism:
*Mulm
Also useful:
dead stuff
2. What everything does in the sand bed
(or I think they do at any rate)
Essential to the FWSB
A good sand:*ABSOLUTELY ESSENTIAL.*A good FWSB*sand doesn't get very packed down and the top layer could be described as almost fluffy. "Fluffy" sand is good for a few reasons. One is that water and dissolved gasses and nutrients can diffuse through the sand more quickly and for greater distances than in packed sand. Another reason is that mulm can more readily sift down into the sand when it disintegrates. Also, worms and snails and other critters can burrow into it more easily.
It's important that things can diffuse through the sand since that's how the ammonia, nitrite, and nitrate can reach the various bacteria which process them and keep the water quality high. Also, it's how nutrients move through the sand and reach the rooted plants.
The burrowing is important because it enhances the movement of nutrients, oxygen, and nitrogen compounds through the sand.
Finally, it is essential that mulm be able to penetrate deep into the FWDSB. Practically everything else can go but for bacteria, sand, and mulm and the FWDSB would still function at least marginally. Take the mulm out of the sand and you'll diminish the function to the point where it is quite unremarkable.
Mulm: ABSOLUTELY ESSENTIAL. Mulm is the source of energy and/or nutrients for the FWDSB. The bacteria which perform all the important chemical reactions, for converting ammonia to nitrates, nitrates to nitrogen, releasing locked-up mineral nutrients, neutralizing hydrogen sulfide, etc. either just get some essential mineral nutrients from the mulm, like autotrophic bacteria that burn NH3/NH4 or H2S for energy do, or they get those nutrients plus they aerobically or anaerobically metabolize the organic compounds in the mulm for energy, as heterotrophs do.
Mulm provides food for the malaysian trumpet snails, planaria, and blackworms, which burrow in order to find their favorite mulm eating bacteria. It also provides mineral nutrients which bacteria unlock so they become available to the root feeding plants in the sand.
When it is getting started up, a FWDSB of the type I describe takes a while to reach its potential since at first there's no mulm to sift down into it. It has occurred to me that a thin layer a mixture, of 5% soil or flour and 95% sand laid down, capped by .25 to .5 inches of plain sand, all on top of the remaining sand bed would kick start the whole process. Or perhaps one could compost some fish food in water, allowing it to decay for a good while and then inject it with a turkey baster directly into the sand here and there.
At any rate, decaying organic matter in the sand is essential. Without it you could have some autotrophic bacteria like nitrifying, which would have to depend on the mineral content of the aquarium water and what leached from the sand to get those elements which are essential to their life. Other than that, not much would be goin' on. Root feeding plants would be at best hum-drum and would need root tabs.
To have a rich, mulmy, sand bed I simply don't vacuum. I don't overfeed and I don't vacuum and I use weak filtration so my filter doesn’t suck up all the good stuff. If I had a more modestly stocked aquarium I would probably slightly overfeed á la Walstad but I've got so **** many fish their poop is plenty.
Rooted Plants: Plant roots not only absorb nutrients from the soil, but they actually can carry oxygen down into the soil to create a microenvironment right around themselves which they can survive in when they penetrate severely anaerobic and anoxic regions. This oxygen facilitates the action of aerobic bacteria much deeper into the substrate than they otherwise could reach.
Some aerobic bacteria which live down amongst the roots oxidize hydrogen sulfide while others metabolize methane, alcohol, and other metabolic byproducts of anoxic and anaerobic bacteria. This way, plants greatly contribute to the safety of deep sand bed regions where toxic gases and chemicals are formed.
Also, plant roots open up the sand as they grow and help keep it from compacting.
Also also, when the plant dies or if it is cut off at the roots, the root system dies and decays, releasing CO2, minerals, NH3/4, and other nutrients back into the soil. Decay is an important source of CO2 in many aquatic ecosystems and it assists plant growth. Ammonia/ammonium is absorbed by nitrifying bacteria to create nitrates and also by many aquatic plants as their favored source of nitrogen. The decaying roots disintegrate and loosen the sand once again.
Also also also, plants absorb heavy metals and other toxins from the substrate before they can leach into the water as well as absorbing such metals from the water column.
California Blackworms: What can I say? They're tops! One super thing blackworms do is burrow from the surface to the start of the anaerobic layer, opening up the substrate and assisting the circulation of and diffusion of water and gasses up and down that first approximate .5 to 1 inch. This helps sustain the anaerobic layer where there is still oxygen, but in very low concentrations and nitrate is reduced to N2 or N2O and is released as bubbles.
Also, the worms eat decaying organic matter and bacteria, transforming some of it by metabolism into energy and soluble waste molecules like CO2 and NH3, which is great for the plants, and breaking the rest of it down into finer and finer particles which are excreted as waste and which can sift down deep into the sand to continue decaying and fertilizing.
Also also, the worms attract loaches and cories as well a some other fish, which go after them so enthusiastically that they dig up the sand. Especially the kuhli loaches, which practically are burrowing - to a depth of about .5 to 1 inch - at times to reach the worms. And, basically, worms are great food for the fishies.
Planaria: What are planaria? They are flatworms, segmentless, flat, worms. They are small, usually .25 inches and less. They eat fine organic matter and bacteria, and will crawl in between grains of sand to do it. Oh, and they a closely related to flukes, which are parasitic flatworms.
Essentially, the planaria go more places in the upper substrate than do the blackworms, which basically stick to their favorite burrow. They barely, if at all, disturb the sand when they crawl into it so they're no help with oxygenation and circulation. What they are good at is taking very find organic matter and converting it into a. more planaria, b. metabolic products like CO2 and NH3, and c. incredibly fine organic matter, which is good because the finer the matter is the faster bacteria will finish breaking it down into metabolic byproducts.
So planaria are a very good though narrowly specialized member of the cleanup crew. Here's an extreme close up of one between 1/8 and 1/4 inch long crawling in my aquarium on the glass (they're totally aquatic so no worries they'll get loose).
Malaysian Trumpet Snails: The good old MTS. If you didn't already know, these guys like to burrow in search of whatever it is they eat. They really do a good job of turning over the sand. So much so that they are seen by some as the solution to the problem of toxic, anoxic pockets in the sand which will eventually release H2S and whatever else and kill all the fish in thirty seconds. The snails are supposed to burrow 'most everywhere and mix up the anoxic with the anaerobic and aerobic sands.
Personally, I don't buy it. I've never seen any sign that my MTS are burrowing deeply enough to mix it up that way. I'd be seeing black sand sometimes appearing on the surface when they surface which I don’t and I see them burrow sometimes next to the glass and they never go even as far as 1 inch down. If anything is protecting my particular FWDSB tank from H2S it is probably the rooted plants (see above)
What these snails do is turn over that important top layer and help exchange gasses/chemicals up and down. They also seem to eat organic matter and microorganisms under the sand so they probably help in a similar way to planaria.
Nonessential but useful for the FWSB
Shrimp: These guys mess around on top of the sand, eating random crud and breaking it down. They also pick up grain of sand after grain of sand, helping small particles of mulm get a start on sifting into the substrate. These li'l guys are nonstop action and I'm sure they get a lot of mulm to start on it's path to disintegration and into the sand.
Kuhli Loaches: These little guys like to dig down into the sand for anything or any reason which pleases them. Maybe for fun, who knows? What I do know is that they love eating blackworms and dig down after them over and over, usually unsuccessfully. So, they do the same thing that MTS do, just faster and less methodically. I suppose if you didn't want MTS and you wanted kuhli loaches , so long as you had blackworms in the sand, the MTS wouldn't be missed.
Scuds: Otherwise known as amphipods, these guys look and act like if you crossed a shrimp with a cockroach. They're quite small and from a distance look just like some random, light colored bug. Amphipods eat small bits of crud and poop out much smaller bits. Basically like shrimp but smaller. They can help break down mulm. Also they make great fish food! Sometimes fish will snap ‘em up faster than they can reproduce though. A lot faster.
Pond Snails: Know as bladder snails, also. They crawl around eating anything tasty, leaf litter, biofilm, old fish food, and god only knows what else. They help break down mulm and stuff which is almost but not yet mulm.
What I use pond snails for is this; I catch them and crush them in my planting tongs. Then I stick the squished snail and its shell a couple of inches into the sand, not far from some lucky plant. This way, the snail has gathered up a bunch of trash and without knowing it, become fertilizer.*
Dead Stuff: Kind of nonessential, but not precisely. Any organism which dies or part thereof is dead stuff. Mulm is not living stuff, and may be called dead stuff but I classify it separately. Anyhow, if a small fish dies, say like 2.5 inches long and under, you can do like I've done and bury it way at the bottom of the sand. Also, you can leave severed but intact root systems in the sand or even bury some plant material here and there, but not too much. This stuff will all decay and create anoxic or anaerobic zones around itself, which is why I say bury it at the very bottom of the sand, three inches down. It will release nutrients into the sand, and gases as well. Be sure only to bury small amounts (like a pond snail or a small fish) at a time and have plants planted close by so their roots will invade the zone of decay and disarm the toxins with their oxygen microenvironment while they make use of some great nutrients.
Nutrients are why one would bury dead things in the sand. Aquatic plants, fish, shrimp, and snails are made of the exact kind of elements needed by aquatic plants! When they decay they release, amongst other things, useful stuff such as CO2, H2O, NH3/NH4, chemicals containing phosphates, iron, magnesium, calcium, trace elements like boron, molybdenum, selenium. The anoxic/anaerobic environment encourages bacteria and processes which release metalic elements such as iron, for example, as a positive ion which plants can absorb readily. The CO2 and NH3/4 can be taken up by the roots as well as it can diffuse upwards through the sand. CO2 will be released into the water where plants will take it up by leaf. NH3/NH4 will be oxidized in the aerobic region into NO2 then NO3 and either released either into the water or to diffuse back down to the denitrifiers where the nitrogen* will be liberated as either N2 or N2O
Placement of dead stuff: Smaller things can be less deep in the sand but I suggest they at least be in the upper anaerobic zone. Larger things have much more tissue - if something looks twice as large, it probably has around four to eight times the volume of tissue. So, a 2.5” fish is much much larger than a 1” fish. Probably it’s twice the height, twice the width, and 2.5 times the length, which gives us ten 1” fish worth of decaying tissue. My experience has been that a 2.5” dwarf gourami’s zone of anaerobic/anoxic decay extended from the very bottom of the sand to within .25” or less of the surface. Anything bigger might break through the aerobic layer and release toxins into the water column. It is in the aerobic regions in the sand bed and surrounding living roots that toxic byproducts of oxygenless metabolism are converted by bacteria into CO2, SO4, H2O and so forth So, if you are too liberal with burying dead things which will decay, you will surely end up with pockets of toxins which overwhelm the capacity of the aerobic layer and rooted plants to neutralize. In other words, you can kill everything or at least foul your tank pretty easily.
I suggest space a 2.5” fish is really a little too much unless the sand is a solid 3” or more deep. In the future, I will stick with 1.5” and smaller. I’d keep a 1.5” fish four inches from the next on, buried right in the bottom of the sand bed. A pond snail I’d try to place 1 inch or even closer to the next. The idea is to have their zones of decay not overlap by much. So a 1.5” fish probably has a zone of intense anaerobic decay that extends about two inches. The* 2.5” fish I buried has one of almost three inches and a milder zone extending out almost four inches.
My favorite dead fish!
I don't believe that the TB is likely to grow anaerobically and emerge from the sand. Especially since it's been like a year and a half that the dead fish has been down there and no other fish in that tank have come down sick with any kind of bacterial illness the whole time.
I had a dwarf gourami which died of fish TB (I think). I buried it deep under the sand about a year and a half ago to see if it would create a scary anoxic zone and also to see if it might make good fertilizer. The fish has been buried for almost eighteen months and still generates several daily flurries of gas bubbles. I think it did create a toxic, anoxic zone but I planted cabomba near it on the theory it would help neutralize at least some of the hydrogen sulfide and other poisons with the oxygen and aerobic bacteria which come with the roots. I also guessed the sand bed would be deep enough that aerobic bacteria in the upper reaches might have a chance on their own to neutralize the poisonous stuff. There is no evidence of poisoning in the tank. I believe that the bacteria in the aerobic layer of live sand and the regions immediately around the cabomba roots are metabolizing the products of anaerobic decay, neutralizing any toxins.

I have included a photo of the area through the glass and circled the place where the gourami was/is in red and also circled a gas pocket in blue.
The root systems of some cabomba can be seen infiltrating the heavily anaerobic possibly anoxic zone of black sand surrounding the dead fish. There's actually a root that is sticking into a gas pocket as I write this. The gas pockets slowly move up through the sand and then release into the water to rise and pop harmlessly. Above the zone of anaerobic/anoxic decay is a very sharp border and only a very shallow aerobic layer of sand. Worms are living quite happily in that aerobic zone, untroubled by whatever is going on below them, which I take as evidence that any H2S or other toxins are not leaching up and out. Also, the cabomba are quite lush, which I think might have something to do with the nutrients leaching out of the poor little fishie. I'm not sure if the worms are contributing much in this case, though. I think they're more handy in encouraging oxygen and nitrate and mulm to diffuse downwards into the anaerobic zone and facilitate denitrifying bacteria (which will operate in very low oxygen but not totally oxygen deprived areas).
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The following is not so much about how FWDSBs work but about how things like FWDSBs are developed and what things hinder discovery and development within the hobby. It is a rant.
One issue I have with our hobby is the plethora of anecdotes and opinions about things, which often generalize the specific: sand beds are dangerous because they'll bubble hydrogen sulfide into the water and it'll kill your fish in a minute is one example - in reality SOME kinds of sand beds can SOMETIMES develop pockets of H2S and clearly there've been a few incidents where when a bubble of H2S or some mystery gas escaped something poisoned the water and killed all the fish quickly, though there isn't proof the poison was H2S, just the correlation of the bubble with the deaths.
I read these sorts anecdotes and opinions all the time online and hear them in the LFSs in the city and they often contradict one another or even contradict known facts. We discourage ourselves from exploring many options with things like the inches of fish per gallon debate and the sand beds are all dangerous rumor. Sure, plenty of people want a standard gravel bed tank with colorful gravel, plastic plants or a few decorative live ones, absolutely zero algae and your basic petshop fish and there's nothing wrong with that and nothing wrong with the water changes, root tabs, vacuuming, and powerful filtering which go along with them if you don't mind them since they're needed for that sort of tank. Neither is there anything wrong with ADA style "nature" tanks or those european planted tanks with all their CO2, nor is there a problem with "El Naturale" tanks. What is wrong is the misinformation and disinformation we all spread to one another which keep hobbyists from understanding the real principles which underlie how the different styles of aquaria work. Those same principles are what underlie the FWDSB I propose.
Those same principles can be applied creatively to develop other variants of aquariums. Sort of like basic ingredients in a kitchen being used to create a number of different recipes.
Thing is, we don't parlay in terms of the underlying principles of aquaria. As Walstad points out, each aquarium is a little semi-independent ecosystem. The principles have to do with biology and chemistry and physics, which can seem a little challenging, but what the heck, so are the principles underlying organic farming, which doesn't require an engineering degree to succeed at. So, one can stick with established styles and techniques of aquaria keeping and not have to worry about having a comprehensive understanding of bacterial ecology, plant nutrition, soluble gases, etc. as long as one sticks with authoritative sources for guidance and instructions like Tom Barr or Diana Walstad or Takashi Amano. Or one can forge ahead, building on the knowledge and experience that precedes, and do so successfully if the knowledge base being built on is sound and one is careful to try to understand what they learn - for example I study
Walstad's "Ecology of the Planted Aquarium," read
Tom Barr online, and a few other sources on
saltwater DSBs and live rock biofilters and have a basic understanding of biology from college and high school biology classes and I asked
Justin at Ocean Aquarium http://oceanaquarium.blogspot.com/how to do one of his style FWDSBs, then put what it all together and learned more by experimenting, measuring and paying close attention to what was happening (should've been taking notes, though) and now I [believe I] have a fairly complete understanding of how my sorta FWDSB works and sure knowledge on how to duplicate what I've already got. Or one can fumble along without deep understanding, being guided by anecdotes, apocrypha, rumors, and uninformed misinterpretations of scientific knowledge all from well meaning people who feel reasonably sure of the soundness of their advice.
That last route, with the anecdotes and rumors rather following good advice or application of accumulated knowledge in accordance with the principles underlying healthy aquaria, just restricts potential for creativity at best, and at worst leads to disasters. Since it's popular to be cautious and conservative, most of that advice is merely restrictive, like the inches per gallon rule or the notion one's filter ought to circulate 10x the capacity of the tank per hour or that deep sand beds cannot work with freshwater. It bothers me immensely to see this sort of stereotyped advice, "popular wisdom." It also bothers me to read the debates such as the one on what is a better guideline or system for stocking a tank. They are full of arguments based not on facts or even good theories necessarily. Just check out all the discussion of stocking - is it about oxygen supply and CO2? How does oxygen best get absorbed into the tank and what about CO2 levels and how to manage them if necessary? Or is it about bioload? Or is it about being humane to fish and what are their healthy behavioral needs anyhow? How do we know what the oxygen requirments or bioload of a fish is? Length? Volume? Mass? Activity Level? How is it known that corys are only happy in groups of six or more? (I have three happy seeming cordydoras harbrosas, by the way, who hang out together and forage and have nice vivid markings and are active - so who's to tell me they're not happy?) or that blue rams definitively need a 20 gallon tank minimum? And does the behavioral approach to stocking a tank take into account its decor, planting, tank format (cube, tall rectangle, column, rectangle, globe, etc.)?
In discussing my FWDSB I'm sure transgress the ideals expressed by this rant, above. However, I do try to discuss the "ingredients" to my "recipe" so that it amounts to "this sort of FWDSB works in such and such a way and does such and such things" rather than lay down a law like "DSBs work in freshwater." For example, my tank has worked well with miniscule power filtration, like 25gph for a 9 gal tank (I think the powerhead is supposed to be 50gph but the flow through the filter is not even really half that), and no vacuuming but I'd never say you should follow that as a rule - what if you were setting up a gravel bed, non-planted tank? No, I can't tell you general, hard and fast rules based on my experience. I CAN tell you the principles underlying the functioning of my aquarium with it's FWDSB and I can tell you how to SPECIFICALLY set up a FWDSB of your own which will work and because I understand the underlying principles, I give you some good advice on what to do if you want a FWDSB like mine except you don't want worms. I don't have to rigidly insist on worms. It can be done differently and the result will work a little differently, possibly have a somewhat lesser biofiltering capacity for example, but it can be done.
It would be unfair of me to give general advice on not vacuuming and weak filtration to people not using an aquarium technique which that works with. Just the same as it is not fair of people to push the sort of general advice we find on FW sandbeds, heavy filtration, fertilizers, stocking levels, etc., when it really only applies to specific cases or is based on principles which the advisor may be quite unfamiliar with.
Thank you for indulging my rant. As a liberated sorta girl who looks up to Diana Walstad for her creative, inventive, and independent thinking in the hobby, I just had to put my two cents in on the sloppy thinking/communicating in case it resonated with anyone out there reading who might then decide they'd like to discover this hobby for themselves, free of restrictive dogma and superstition.
Coming up soon: A step-by-step description of how to set up a FWDSB, with a list of the specific plants as well as the critters I've already said I use. This all minus the dopey experiments like burying gouramis. I'll list and briefly discuss the chemicals I add to the water, like Excel for BBA once in a blue moon and Seachem Neutral Regulator, Discus Buffer, and Equilibrium. Though I don't believe they're needed, I do use them and they do work.
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As for regular water changes, I model my schedule after what Walstad describes in "Ecology of the Planted Aquarium," since her and my styles share heavy planting and extensive biofiltering in the substrate beyond what basic nitrifying bacteria based biofilter schemes accomplish. The idea being that the water is naturally purified by those plants and substrate.
I'll be the first to admit Walstad (and thus my) practice is at extreme variance with popular approaches to water changes. But there are other aquarium styles which don't change water at all except in emergencies/medication issues! The (very nearly) self-contained, balanced tank is one style kept in San Francisco and probably elsewhere at least where the aquarium is merely topped up once in a while. Generally they've no artificial light, no feeding either. Very low stocking levels, though.
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How to set up a FWDSB tank a lá DeeDeeK
First let's review: What goes into my deep sand bed?
First of all, there is sand: I recommend the kind of sand I use, which is a quartz based, fairly smooth grained (as opposed so sharp grained sand - which will hurt your cories btw) sand. What I get is a river sand. It resists packing tightly and allows dissolved gases and nutrients to diffuse through the sand quickly and for good distances, and also allows disintegrating mulm to sift down into the sand. And it's easier for critters to dig in it. What I get is a river sand that the guy at my LFS pre-washes and repackages so I haven't figured where to procure the stuff on the cheap.
An easy source of sand is Caribsea. They carry many different kinds, including a nice river sand called Peace River Sand. I DO NOT recommend using the plant growth substrate media Caribsea sells (like ecocomplete), their sharp grained sands (they label smooth grains “safe for belly crawlers” or something like that) or gravel for use with the FWDSB.
There are four primary organisms in which I put in my FWDSB:
I tend to say they're essential, but truly it is only their functions which are essential - so long as the function is being accomplished somehow, that's all that truly matters.
Rooted plants
California blackworms
Planaria
Malaysian trumpet snails
In addition, I've added some other organisms to contribute at times but I don't think they're needed:
Tiger shrimp and Red Cherry Shrimp
Kuhli loaches
Scuds
Pond snails
Further, there may be any number more of useful critters but I just don't know of them.*If they fulfill the functions of oxygenating sand, breaking down mulm, or neutralizing toxic compounds, then they'd be very useful and possible substitute for one of the "essential" organisms.
I've been using the following chemical additives:
Flourish Excel (to poison BBA, which cropped up on my driftwood and java moss and returns periodically - not really a bad case but I hate the crud). I am not enthusiastic about handling and exposing my fish, self, and family to a chemical which is known as a BIOCIDE. I’ve overdosed the tank before at approximately 15ml/9 gallons and had shrimp deaths and the fish gasped at the surface until I did a 40% water change. At 10ml/9 gallons I think the shrimp were ok and the fish seemed fine.
Neutral Regulator, which is a phosphate based ph buffer, which sets the ph to 7 or very close to it, plus conditioners that neutralize chlorine, chloramines, and ammonia. I use it to condition tap water prior to adding it to the tank, in conjunction with Discus Buffer to set my ph where I want it, which is 6.4 recently but usually has been 6.8, which is a great ph for planted tanks in general (with many exceptions).
Discus Buffer, which is another phosphate based buffer which adds acidity when combined with Neutral regulator. It also precipitates calcium and magnesium from the water so to restore hardness and mineral content I add Equilibrium.
Equilibrium is a water hardness additive/fertilizing formula of Magnesium Sulfate, Calcium Sulfate, Potassium Sulfate, Ferric Sulfate, and Manganese Sulfate. Raises GH without messing with KH or ph. I set my tank water to 5GH and ignore KH (maybe that's foolish of me?)
Kent Marine brand Iron and Manganese is a micronutrient supplement I used when I first got the FWDSB tank going. It supplements not just iron and manganese but also potassium, molybdenum, and cobalt (which I’m not sure is needed, but there you have it). Though Equilibrium has some of these, I supplemented because they are absorbed fairly quickly and I was concerned the micronutrients Equilibrium added would be exhausted before sufficient mulm had built up for vigorous plant growth and Kent Marine’s brand seemed as good as any other. I like that the metal in Kent is in the form of ions bound with EDTA, which releases them in the presence of light, so the leafs can take them up readily.
I say these chemicals are not needed though I've used them the whole time I've had this FWDSB setup. I prefer the greater sense of control and stability I feel when using them. If you do want to use them as I do in my FWDSB tank, follow instructions on the labels to set ph to 6.8 and GH to 3 to 6. If you plant heavily to start with, it may be worthwhile to use Kent Marine Iron and Manganese drops, but you can probably save your money. Save the Excel for BBA outbreaks, should any happen, dosing the tank at 1ml/gallon or less. I've lost shrimp at 1.5ml/gal The FWDSB once established will contain plenty of decay releasing CO2 from its depths so no need for expensive, toxic Excel as a carbon supplement. If you feel you must dose with Excel, do so. I'm just personally a little scared of it.
A note on Poop: Fish Poop is not a chemical supplement but as far as fertilizer goes, fish poop has the same elements as are in fish food, made from algae, yeast, fish, and shrimp, which together have all the micronutrients a plant needs, as well as the macronutrients N, P, and K, as I understand Walstad to be saying in "Ecology ..." So the sand bed will become more and more fertile as the fish eat and poop and the mulm sinks into the sand. There isn’t much call of Equilibrium or Flourish or Kent Marine brand Iron and Manganese drops or other fertilizers.
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Setting Up the FWDSB aquarium a lá DeeDeeK:
So, you get a fish tank. Get sand and wash it, then fill the tank to approx 3 inches depth with it. Fill it with water and water conditioner (I use Neutral Regulator).
If you want, add other chemicals.
Put an internal filter rated for half at most the size of the tank; a weak filter will allow the mulm to settle down where it will decay and disintegrate and sink into the substrate, which is essential to the FWDSB. A simple powerhead with a sponge filter is adequate. Do not use aeration! It will blow off all the CO2 which the substrate put there in your water. Position the outlet of the filter/powerhead such that it disrupts the surface layer/ surface tension but not violently. Smooth roils and ripples will suffice. This will create very good aeration. Bubbles don't really add much oxygen to the water.
Add a heater if this is to be a warm water tank. I don't know how the FWDSB would work in coldwater but I bet it's similar but maybe with less capacity as a biofilter. I keep the water at 80º because I have a Blue German Ram and he's sensitive. Otherwise, I'd keep it at 77º.
If you can, use a turkey baster or whatever to suck up/scoop up a nice sample of sand from an established FWDSB tank or an established planted, sand substrate tank's sand. squirt/pour it all over the tank and stir it into the substrate.
Cycle the tank. I recommend using fish food with no fish or other animals present. Put pinches of flake into the tank just like you were feeding a full tank of fish. Start with a nice, fat, fat pinch Let it sink and decay. Measure NH3/NH4 daily and "feed" a regular pinch daily until the goal concentration of NH3/4 is reached, then stop feeding (the food remaining in the tank will continue to produce NH3/NH4) and proceed as usual when the NH3/NH4 starts coming down from its peak. Measure for NO2 as well as NH3/4 now and continue to monitor the levels until they reach zero. This method gets mulm to start forming and gets your sand bed off to a head start in terms of fertility.
Or cycle the tank with any other method you like instead if you feel unsure about the fish food approach. But remember that the fish food method gets mulm off to a good start pre-planting and stocking.
Once cycled, you can place driftwood and decor and plant your plants. I recommend starting with a modest number and propagating plants yourself over months as your tank matures, landscaping as you go. This is because the DSB isn’t very fertile yet and doesn't need lots of root systems to oxygenate its depths, and it's so much cheaper (and more fun) to play gardener and propagate plants. You'll have plenty by the time the DSB needs them.
I planted Eurasian Milfoil(the bad milfoil, NEVER release into wild), Northern Watermilfoil(good kind, native to US), Pennywort, Java Moss, Variable leafed Water Hyacinth, Cabomba Caroliniensis, and Dwarf Hairgrass. I have Duckweed on the surface and Riccia floating below it. The Cabomba and Water Hyacinth develop large and rich root systems. These plants have worked well for me together but any plants which include extensive and deep root systems are great.
Now add a tablespoon of california blackworms per ten gallons, a handful of Malaysian Trumpet Snails, some planaria if you can find 'em in someone else's aquarium. I got mine from my LFS. It would be cool to add some shrimp, scuds (amphipods), and maybe some pond snails if you by some miracle don't already have pond snails with your plants. If you like, add one or more assassin snails but watch out that they don't overwhelm your MTS and eat every last one of them. Assassin snails like to dig into the sand a bit and hang out half-buried, so they contribute to the DSB directly as well as controlling the overall snail population. Once you're ready for fish, you might think about getting kuhli loaches, or any other fish which will dig after worms and turn over substrate but won’t mess up your plants.
I'd let the inverts all sort of settle in for at least a couple of days, maybe a week without fish present yet- let the shrimp figure where they wanna hide, let the worms dig in, the planaria to disappear into whatever it is they disappear into.
Now add fish. I go by the
equivalent of about three or four to five or six Endler's Livebearers per gallon as a maximum depending on the level of activity of the fish. One can generally stock far more fish than most conservative stocking guides and rules of thumb indicate. I estimate how many times a male Endler's Livebearers size each given fish is. For little fish I give one gallon for each equivalent of three Endler's, so if there are three of some sort of fish which are the same size as an Endler, I give 'em a gallon. For bigger fish, which are less hyper and have lower oxygen demands, I'll give a gallon for each equivalent of five or six male Endler's Livebearers. I mean, aesthetically, that is too many fish for me, but if the fish being stocked are compatible with one another they'll be fine because they'll have enough oxygen if the surface of the water is being stirred up and the surface tension disrupted by the power filter. Their waste will not overwhelm a healthy, mature FWDSB so long as you don't overfeed. Maybe get an O2 test kit in order to keep track as you add to the bioload so you remain safely within healthy O2 limits.
Time to put on the canopy and lighting. Your it's choice so long as there is sufficient light for the species of plants you choose. I have an 18w PC lamp with a 12000K spectrum for a 9 gal tank for 2wpg. I recommend 5500K to 6700K spectrum daylight tubes; I just haven't been able to find one such 18w PC tube locally and had to settle for this silly blue-white light. Between the fertility of the established FWDSB and the brightness of the lighting, the plants in my aquarium grow like mad. Even Variable Leafed Water Hyacinth, which is said to require 3wpg+ and rich substrate or it will just turn black an die, grows rapidly in my setup. No need to inject CO2 - decay in the sand releases plenty of it which roots take up and which also diffuses up into the water column where leafs can take it up. Maybe get a CO2 test kit so you'll know if you'd prefer to supplement it, if you're not satisfied just to observe the growth of your plants. I'm moving up to 3wpg soon with a new tank and bet there'll still be no need to supplement CO2.
I run my lights 12 to 14 hours a day. My tank has a minimum of that green spot algae and one part of my one piece of driftwood has some BBA. My pennywort's older leaves get green spot algae. Other than that, I haven't had an algae problem despite all the light.
There, that's it I think. Happy FWDSB-ing
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Variants of FWDSB tanks.
Many variants of the FWDSB will work, so long as they're based on the underlying principles that make FWDSBs work as follows:
a) Diffusion of nutrients, toxins, and gases through the sand; this requires the sand to be open. For the sand to be loose and open, it must be fairly large grained and/or opened up and turned over by organisms. For nutrients to enter the sand, mulm must be allowed to settle on the bottom and disintegrate
b) Bacterial populations requiring different levels of oxygen from fully oxygenated to anoxic must not be disrupted too much.
c) The organisms, both microbes and multicellular, exist in a balance like a mini-ecosystem, expanding and improving the environment for each to execute its function.
So we need a substrate which allows good diffusion, bacteria which process waste and neutralize toxins, and larger organisms which expand the depth and range of anaerobic and aerobic bacteria by opening up the sand and also by transporting oxygen downwards (roots), and organisms which facilitate the movement of nutrients downward by breaking down mulm
Operating within those principles, all kinds of FWDSBs can be set up that get the job done.
If you don't like worms, don't add 'em. The plants and snails will work fine, just the biofiltering capacity of the DSB will probably be lower since it won't have hundreds and hundreds of worms burrowing down to the anaerobic/aerobic boundary, creating little burrows from the surface to the anaerobic layer.
If you don't want snails, don't add 'em either. The plants and the fact that the sand is a very loose packing type (you did get a light, large grained sand, right?) will ensure the bed functions. Again, capacity to biofilter will be diminished and mulm won't break down as quickly, so it may build up.
Now if you don't want plants, I'm not sure what to say. You'll need something to help oxygenate deeper levels and to neutralize hydrogen sulfide, and to keep the sand open. I'd say a FWDSB without plants at the very least will not accomplish many of the tasks one sets up a FWDSB for. which can include biofiltration of ammonia to NO2 to NO3, denitrification, providing a fertile substrate for rich plant growth, diminished need for water changes, elimination of vacuuming, and neutralization of toxins which accumulate beneath sand beds.
If you don't want planaria, or you can't find any, don't worry too much. The planaria's role is to further disintegrate mulm which aids it's descent into the deeps of the sand bed, so they're no help with oxygenation so mulm will disintegrate more slowly and perhaps migrate downwards through the sand more slowly. Probably shrimp and pond snails would help significantly in the planarian's place.
Deeper sand works but I haven't seen any which are deeper than 3" which are actually doing anything beyond what 3" of sand accomplishes.
Different grades of sand (and possibly very fine fine gravel can be used to create a sand bed-like gravel bed) can serve the purpose. They will vary in how quickly nutrients, toxins, and dissolved gasses can diffuse into and out of the sand bed's various regions. Also larger grain, looser sand will let mulm into it's depths more quickly. Smaller grain sands will make more mulm tend to stay on top and will tend to pack down tighter and need more plants and critters to keep it open. Perhaps looser sand is better for deeper beds, if there is any reason to go past 3" or 4".
Bear in mind that the above variables affect the biofiltering capacity of the DSB and therefore the stocking capacity of the tank. One can generally stock far more fish than most conservative stocking guides and rules of thumb indicate. I estimate how many times a male Endler's Livebearers size each given fish is. For little fish I give one gallon for each equivalent of three Endler's, so if there are three of some sort of fish which are the same size as an Endler, I give 'em a gallon. For bigger fish, which are less hyper and have lower oxygen demands, I'll give a gallon for around each equivalent of five or six male Endler's Livebearers. I mean, aesthetically, that is too much for me, but if the fish being stocked are compatible with one another they'll be fine because they'll have enough oxygen if the surface of the water is being stirred up and the surface tension disrupted by the power filter, and their waste will not overwhelm a healthy, mature FWDSB.
Of course, the above stocking guideline system of Endler Equivalents/gallon is just another seemingly arbitrary method. The idea is that going by volume of the fish and taking into account the differences in metabolism/oxygen demand per body mass between bigger and smaller fish one can come closer to knowing the true limits of the tank for stocking. My fish aren't gasping and they're active and healthy in my current tank, which is bursting at the seams with fish right now. By the inch of fish per gallon rule, my fish must be dead because I've go like two FEET of fish in nine gallons. Fortunately, they're tiny. Really, though, they will look much much better and probably be less stressed in the bigger tank when I get it.
Shrimps and other invertebrates are a healthy choice for stocking. They tend to enhance the FWDSB by sifting through the top layer of sand and munching on mulm and leftover fish food, creating smaller particles which can sink into the surface and decay faster.
Lighting can vary considerably. So long as there is enough for the plants to thrive, it doesn't probably matter. With 2wpg PC lighting in a fairly shallow tank, my plants grow like they're in a 3wpg setup, I mean they scream! Apparently there's enough CO2 in the water from decaying mulm to support heavy growth. Many Natural Planted Tanks have weak or no artificial lighting and get theirs from the window. With the FWDSB this is possible, too. Personally, I prefer nice bright, artificial light.
Mechanical filtration needs to allow mulm to settle and disintegrate The gunk must get down and stay on the sand so it can sink in and contribute as a fertilizer and food for the microbes in the substrate so therefore it mustn't be too powerful. With that one qualification, any power filtration will do from powerheads with a sponge on the intake to canister filters (though with a FWDSB, canister filters and any other filter packed with biomedia seems redundant). Essentially, water must circulate so the surface is constantly turned over for maximum absorption of atmospheric oxygen and sometimes there is too much mulm or too much suspended crud so mechanical filtration is generally called for.
Size variants. The FWDSB aquarium can be almost any size. My first one was five gallons. A friend of mine has a variant DSB with just plants and no critters in the sand and he has it in a 60 gallon tank. A filterless variant can be done in a gallon container with a few shrimp, plants, worms and a snail.
Style Lots of aquarium types involve a style, like ADA aquaria, El Naturale aquaria, etc. A FWDSB is a FWDSB regardless of appearances. I am into naturalistic but composed aquascapes and have an arts background but don't put too much emphasis on the art of landscape arrangement. There's no reason you couldn't set up an ADA lookalike using a FWDSB tank. The only barrier would involve the differences in species using CO2 infusion allows.
Other substrate variances One isn't restricted solely to pure sand! Why not add 5% potting soil to the sand and cap with .5" of pure sand? Or throw a cup of flour into every ten pounds of sand? The soil and the flour will undergo processes of decomposition and give the DSB a leg-up. Soil especially will be good because it has already a great community of specialized bacteria and microfungi in it. Really, you can do anything with the sand, so long as it is able to function properly as a FWDSB. Add some gravel or even ecocomplete so long as the sand dominates and is able to do its thing as a biofilter, planting medium, waste processor, etc.
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I suggest looking up the Barr Report online and reading that informative site, especially about Barr's Low Tech planted tank
Also, of course, Diana Walstad's book "Ecology of the Planted Tank."
And look up live sand, deep sand beds, and live rock, in saltwater forums
