Freshwater Deep Sand Bed (DSB)

[anorth_uk]

the O2 gets used as it passes through the upper levels of the substrate, hense the low O2 area beneath this where the bacteria uses the NO3 (Nitrate) to get it's O2 from

 

[anorth_uk]

in animals the amount of CO2 regulates how fast we breath, assuming this is the same for fish enough O2 and too much CO2 would just make them breath faster, they wouldn't need to gulp as there is enough O2 in the water. I'd expect the fish to be at their normal level just breathing faster in this situation. (this thread is getting too long to keep flipping up to check what's been said before)

Bio Safe, think I need to find someone that has some as smallest quanity they sell is for 1.5 years lol - would last me forever plus a few centuries.

From reading about Nitrate Reactors and setting them up, I'm beginning to think there may be an imbalance somewhere, almost like one part is working too well, or one part is failing - Nitrate Reactors are very balanced, they do not like wide variations in water quality as the bacteria blooms or fails, one of the reasons they have to be checked so often.

The internal filter should be moving more water than an air stone, therefore O2 should be ok throughout the water column, bubbles only really get rid of CO2 in this instance, therefore we keep coming back to too much CO2.

Had a quick look on the net and the Rena Filstar has a throughput of 220 litres per hour (approx 48 UK Gallons) A 29 US Gallon tank is 24 UK Gallons, so the throughput of the pump is 2 water changes per hour, this sounds low to me - so it may be the water starting to stagnate due to low water movement espically as it is heavy planted, therefore the air stone IS helping the water flow.

atm we have far too many variables and too many unknowns

The oxygen requirements of fish vary considerably, depending on different factors. These include the size of the fish, species, the temperature of the water, quality of the water, the amount of food the fish is consuming, how active the fish is, and so on.
The oxygen demand of a fish can easily double a few hours after feeding, as it uses energy for digesting and processing its meal. Temperature can have an even more dramatic effect, as numerous studies have shown. For example, a 23g Channel Catfish needs approximately 2.53mg of oxygen per hour at 1.7°C, whilst at 18°C it needs nearer 8.46mg per hour, more than a three-fold increase (source: Lawson, 1995). In some cases this effect may be even more profound, for example a Goldfish may have an oxygen demand 6 times higher in the summer, than in winter. In most cases, coldwater and pond fish need an oxygen level of at least 6mg/l, whilst tropical fish need 5mg/l. However, levels should ideally be maintained at 7mg/l. Although small fish require more oxygen per unit of bodyweight, larger fish require greater overall quantities. Therefore, they are usually the first to suffer when levels fall below optimum

Temperature: This has perhaps the biggest effect on oxygen levels. The warmer the water is, the less oxygen it is able to hold. Combined with the increased oxygen demand of fish at higher temperatures; warm water can quite easily become oxygen deficient. The following table lists some oxygen concentrations at different temperatures:
Temperature (oC) Maximum Oxygen Content (mg/litre)
10 11.28
15 10.07
20 9.08
25 8.24
At very low temperatures, or if the temperature falls very rapidly, the ability of the fish to remove oxygen from the water can be impaired, making oxygen deficiency a possibility. However, in most cases fish are able to adjust to falling temperatures in time to avoid harm.

Tetratest do kits for both disolved O2 & CO2, it may be worth investing in these two to see if we can remove two of the variables

Sorry for the abstract comments, but my head is starting to hurt lol

 

[Anoxia]

Wow, I went to the LFS, and I come back to find all these complex things going on here. My brain hurts, too! For now, I am blaming the CO2 excess on too much mulm under the DSB, please feel free to prove me wrong.

The guy at my fish store http://www.aquatouch.com/ said the same thing DeeDeeK says, that I still don't have enough surface agitation. I'm going to go ahead and do the waterfall thing today, instead of waiting for my fish to get better first. He sold me some Ampicillin for my rainbows, with instructions on how to mix it with their food. Hopefully my beneficial bacteria will be OK. I'm really kicking myself for not having a hospital tank about now. Apparently columnaris is really common for rainbows under stress, such as the stress falling out of your aquarium into a box of odds and ends might cause. The LFS also inspired me to attempt a bit of a carpet effect with some riccia or marsilea at some point.

 

[anorth_uk]

Not sure a carpet effect would help, if it obstructs the migration of disolved salts then you could end up with a very toxic area of DSB, then any disturbance of that area would release all those toxins into the water column.

I'm comming to the conclusion that you've had a "big" change in water conditions and the bed just needs to adjust to them, either by parts ramping up or down the amount of work they need to do.

Culling the snails should help, less O2 being used and less waste being produced.

Yes a hospital tank is a good idea, something I'll need once the fry have been moved into my new tank and the existing tank converted to a FWDSB - considering fresh water clams & shrimps in the DSB now as well as the MTS

 

[Anoxia]

Oh, I just wanted a carpet of plants because I think it's pretty, I wasn't hoping it would help with my excess CO2 issue. You really think it could cause trouble? Maybe I should try it in a small area first, and see what happens. I was recently suprised to find a little wad of riccia floating in my tank. I guess it came in with some other plants. I need to find out if riccia will form a carpet. If it does, I will try doing that when it gets big enough.

The biggest change to my aquarium was the addition of the DSB on top of my gravel, smothering the old aerobic bacteria, and causing a new nitrogen cycle. If I had it to do again, I would have removed the gravel first. I think I'd just go with potting soil and sand. I am trying a lot of new things I've never done before, like live plants, and a canister filter, and new lighting, and leaf litter, and keeping worms in the tank. That's why it's hard, when an issue pops up, to pinpoint the cause. Too many variables! Right now the tank, being a DSB tank, is supremely stable, I'm just fiddling with it (with help from others, especially DeeDeeK) to figure out how I can turn this annoying air pump off for good.

 

[DeeDeeK]

DeeDeeK,

Measuring CO2 directly is pretty easy with a ph & kh test kit.

I found this article on measuring O2 level in water, though it requires some additional stuff.

Absolutely! However, Anoxia and I both seem not to have access to the right test kits (my case is due to improper circulation of currency through the DSB I call my wallet(yes, there is mulm at the bottom of it)). Additionally, an measure of concentration alone will not tell us if the fish are receiving too much or too little O2 or CO2; the behavior of the fish can be correlated with the concentrations of those gasses or with conditions conducive to adequate, inadequate, or excessive levels of said gasses. Hence the examination of fish to see whether they're gasping or happy with various circulation scenarios.

I'd MUCH prefer to just use a couple of test kits! Thanks for the info and the links!

I have a question: one of the alleged benefits of a DSB (as I understand it) is reducing nitrogen compounds with anaerobic bacteria. In my simple mind, there is a paradox that I can't resolve with this scenario. First, it seems to me that the exchange of water through the DSB would seem to be non-existent deep in the bed. There is no real mechanism for that to happen. But, let's assume that there is some interface level where there is ample flow to feed in fresh supplies of nitrogen and other compounds needed, but deep enough to be anaerobic. Wouldn't the same flow that pulls the nitrogen compounds to the anaerobic interface also carry with it dissolved O2, which would, by definition, make it not anaerobic? Or is there some process by which O2 is pulled out at it descends through the sand bed and is mostly void of oxygen before getting to the interface?

H2O molecules will circulate only very little, if at all, in the sand bed because there is nothing driving it to move. However, if a compound such as NO3 or H2O is present in one area and less or non-present in another, both areas being within the same body of water (let's say a body with no circulation), molecules will tend to move into the area where they are absent or present in lesser concentration until there is an even concentration. So, water molecules will move within the sand bed in one direction while a solute moves in the opposite. There, a VERY simplistic but accurate description of my personal mis-understanding of diffusion, partial pressure, etc. Just think that all molecules of any one kind within any one medium (water or air for example) want to go everywhere in equal numbers relative to one another and exert pressure against any barrier holding them back from regions where there are fewer of their own kind so they'll spread evenly throughout. If there were much actual movement of water, flow through the sand bed, it would interfere with regions usefully segregated by oxygen concentration from establishing themselves with their various bacterial entourages.

I know what I'm saying has been more clearly put by Anorth_UK but sometimes it's useful to read it put differently in a different "voice," so I hope this posting is more helpful than the inaccuracies contained herein are harmful.

Here's a thought: In the upper region of the DSB, the sand is looser, with larger interstices and therefor easier infiltration by solids and more rapid diffusion than the deeper regions have. Through this aerobic zone, all organic matter, dissolved or solid, on its way down must pass, where it will decay aerobically. Add to that aerobic ammonia, nitrite, sulfide, methane, or hydrogen eating bacteria (many of them autotrophs). By definition, the aerobic region is that region where there is enough O2 for aerobic metabolism, so that zone will be as deep as needs contain enough aerobic activity to consume almost all the available O2.

If the sand is loose enough and shallow enough and the supply of organics and dissolved gasses low enough, no anaerobic or anoxic zones will form. You could make a titanic aquarium with a substrate of stones the size and shape of hen's eggs but sufficient depth that the bottom is completely anoxic so long as no current is driving fresh water down into it. You could make a biofilter-type substrate bed aquarium with clay or silt as a very shallow substrate and still have nice, gooey anoxic and anaerobic zones, as well as a very shallow (I hypothesize) aerobic zone. (You wouldn't believe the surface area of clay! Incredible, plus the particles are generally polar so bacteria really like sticking to them! I'm a ceramist and I can tell you the difference between aged clay, where bacteria have formed a thorough and gooey biofilm over all the particles, and clay freshly mixed from dry constituents can be extreme in terms of plasticity and wet strength! Massive gooey biofilm! Clay can be an extremely effective biofilter medium, but that's for another thread.)

Anyhow, given a deep enough substrate of small enough interstitial space with sufficient influx of material for the resident bacteria to oxidize, there will be underlying the aerobic region an anaerobic and possibly an anoxic region. O2 will diffuse from area A to area B at a rate determined partly by temperature and by differential in concentration as well as by the distance it must travel and the volume that may travel through that distance (through the sand bed, around grains in the limited space in between them is a twisty, narrow path) and no faster so at some point consumption will overtake supply given a long enough (deep enough) path for the O2 to travel.

Below the aerobic level, there are anaerobes which use NO3 to oxidize all sorts of things. There are heterotrophs, which use the Os they remove from NO3 to burn up sugars, proteins, oils, etc., and get their complex organic molecules from the same source as their fuel-mulm. THEN there are autotrophs, which build their own complex organic molecules from CO2, H2O, and mineral sources for the chemical elements they need like iron, sulfur, boron, etc., just as do plants except they don't use photosynthesis to power the process but use the energy they gain by oxidizing, in my favorite case, hydrogen sulfide!

So, H2S diffuses upwards from below, where sulfate reducing bacteria and bacteria anaerobically breaking down sulfur-containing organics like protein produce it. Nitrate diffuses down from the aerobic, nitrifying bacterial bed. CO2 is practically everywhere from everything in the aquarium, water is omnipresent there, and the mulm releases mineral nutrients in excess of what comes from the water and the sand. If all goes well, H2S never builds up excessively in the sand bed, nitrate is drawn down into the bed by a differential in concentration between the aerobic layer/water column and the anaerobic layer(s) and organics continue to be consumed such that the mulm becomes mineralized (and hopefully absorbed by plants) and the sand bed doesn't become clogged for a VERY LONG TIME, while becoming ever more fertile.

I must point out that the sand bed becomes more compressed as it gets deeper, so NO3 doesn't move as quickly into the anaerobic region to be consumed as, say, NH3/NH4 does into the aerobic region. A very easy balance to achieve in the freshwater DSB is one where NO3 production outstrips NO3 reduction. The more evenly meshed the sand (therefore having a smaller size range of grains) and the more spherical the sand's grains shapes are, the more resistant to compaction with depth it will be and the evener the rates of diffusion will be across depths. In other words, get pool filter sand or evenly meshed riverbed sand (rounded grains, y'know) or horse racing track sand (carefully compounded to resist compaction over repeated poundings by hooves and wheels) without needing to be constantly graded and raked). Use one of these good sands and you'll get a deeper aerobic region and excellent NH3/NH4 & NO2 removal, be less dependent on burrowing critters and plants (though I consider plants all but indispensable unless you have a DEEP DSB with really fluffy sand), and better NO3 reduction so long as the bed is deep enough.

There are theorists, I can't remember who clearly but I promise these are not "straw-men" I am knocking over, who have stated one would need either a ridiculously deep DSB or absurdly finely-grained sand to achieve nitrate reduction in a freshwater DSB. I've never found the actual source so I don't know the basis of their hypothesis but I've found casual reference to such assertions in my even more casual reading - sorry to be apocryphal with this. So I mean to say that somewhere out there, there are doubters who have presumably thought this idea through pretty well as well as many of us (and I was of this camp once) who accept as received wisdom that DSBs will not work in freshwater.

It's good to read from a person who has some clear objections/concerns and voices them so well. It provides an opportunity to rethink or think-about-in-the-first-place important basic concepts as well as their many corollaries when answering, rebutting, or even (gasp!) agreeing said objector/concerned party. In short, thanks for the questions and objections! Great stimulus for the verbose and grandiose writer such as yours truly.

I'm thinking of making a spreadsheet with every element, concept, hypothesis, presumed fact/strong theory, or relationship between the prior items in this list in it. Why? So at least an electronic brain can hold the whole thing together and not forget what things are affected by what and how that those relationships work. I'd like to be able to see the broad picture and how it generally changes as variables are added, removed, or changed.

Please pardon the thinking "out loud," but when I'm triggered to write a bunch by what I read in a thread, I gotta do it right then! Otherwise I just fill my mind with thoughts like "what the hell is killing and eating my bumblebee shrimp and rcs shrimplets? Is it planaria? They seem to attack and sometimes kill blackworms...I wonder if there were enough of them in a bathtub and I got in ...fizzle, pop, click," or "should I reheat that beef brisket from last night for lunch today?" Oh, yes, true thought of mine.

I actually go back and cut 'n' paste my postings and my favorite postings of you, my aquariacentral friends, into long rambling documents which I refer to in further writings or other projects!

 

[Anoxia]

This is probably the worst aquarium picture ever, I didn't even clean the glass or anything, but I'm just hoping to show the amount of water flow going on now.

There's duckweed floating around the rainbowfish, that's how far down the water pushes it, then the duckweed floats towards the sides of the aquarium, and back up. I can't get more water flow than this without buying an HOB filter, so I really hope this does the trick.

I mixed the Ampicillin with flake food like I was told, and fed it to my rainbows, but I regretted it almost immediately. Seeing all my little fish buddies, trustingly picking their morning meal out of this white chemical cloud I had dumped in there, something felt wrong about it. It goes against my hippie nature, or something. I'm not going to do that to them anymore. I'm just going to keep the water as clean as I can.

The air pump has been unplugged for an hour, so far, so good!

Edit: I just saw your post, DeeDeeK, you must have put it up while I was typing! I don't have time to respond right now, I have to go, but I will as soon as I get a chance.

 

[anorth_uk]

Those theorists have now become part of the hobbies fairey tales and are held up as gospel. Really happy you are both proving them wrond

When you get the spreadsheet sorted I'd like to have a look at it

My DSB will be 6-7" deep so will need to grade substrate, found out today that MTS only graze the top 2" of the substrate and marine DSB's have a 50% sand change every year

The rest odf the post's I'll go over tomorrow as it's hard to type on this netbook

 

[DeeDeeK]

Those theorists have now become part of the hobbies fairey tales and are held up as gospel. Really happy you are both proving them wrond

When you get the spreadsheet sorted I'd like to have a look at it

My DSB will be 6-7" deep so will need to grade substrate, found out today that MTS only graze the top 2" of the substrate and marine DSB's have a 50% sand change every year

The rest odf the post's I'll go over tomorrow as it's hard to type on this netbook

The local San Francisco practice of freshwater DSB keeping does not involve sand changes at all. Probably because they're almost always well planted; possibly either the trouble of uprooting and replanting plants or some effect of the plants themselves within the sand bed makes it undesirable or unnecessary. Or maybe muck which works its way into the freshwater DSB breaks down more fully due to generally coarser sand or different bacterial, archaea, and fungi species in residence within. Or probably I am shooting in the dark here.

All I know is I've known folks to keep aquaria 15+ years with nary a change of sand.

By the way, anorth_uk, welcome to the forum! I'm so glad to be reading posts such as yours.

 

[Anoxia]

Why would they change half their sand every year? That sounds counterproductive, and hard to do. Wouldn't they have to start the nitrogen cycle all over each time? I know the tide moves sand on the beach, but a marine aquarium isn't supposed to recreate the beach.

So, its been 4.5 hours, and still no signs of too much CO2! Everybody in my tank looks great. The duckweed is still circulating around, but that's far easier to live with than the groaning noise an air pump makes. I can always try to remove the duckweed if I get tired of it. Though I hear that's easier said than done.

I'm happy you are researching clay, DeeDeeK, I am excited to see what you find out about it. I heard it helps the plant roots uptake things like iron and stuff, because it has good CEC (something Cation Exchange? I forget). Have you seen "Miracle Mud"? That's cool you are a ceramist, I am a sculptor. Here's a sculpture I'm doing:

Oh, it turns out Riccia is totally common as a carpet plant, so that shows how much I know about live plants! I don't think I'll use it for that purpose, though, as apparently it wants to float all the time. Constantly trying to keep it down would get real old after a while.