Freshwater Deep Sand Bed (DSB)

I've read this thread a number of times today, also DeeDeeK's threads and several others on the net.

A couple of thoughts,

If O2 is reducing and CO2 increasing that would indicate too many things using the O2, you have said above that you have a lot of snails, maybe a cull of these would help.

Also the DBF is also producing CO2, this area of the filter could be running too efficiently (no idea how you could reduce this)

How long do you have the lights on? plants use CO2 in daylight and O2 in low light levels.

Turning the air pump on and off could also be counter productive. With no water agitation, partial pressures and thermal currents will set up in the tank - obviously aided by the fish movements - plants will obstruct this flow. Turning on the pump will then change all this and it will take time for new flow pattens to establish - the more obstructions in the tank the longer it will take for this flow pattens to establish.

From memory (it's been a very long time since I did chemistry at school) sulhpur compounds tend to be acidic, therefore shells in the substrate will act as a Ph buffer, something I really need to look at for my filter as it'll be for a cichlid tank which needs around 8-8.5 Ph
 
Flow patterns, that's a new idea to me. I have a canister filter (Rena Filstar) with a sponge "prefilter" on the intake, so when the bubbles are off, the water does circulate, just not strongly. I need to make a little waterfall effect with the spraybar, maybe if I just lower the water level until i hear trickling, that will be enough surface agitation to allow me to try it without the air pump once more. I might wait a while on that, though, because I have a fish with a fungus on his mouth at the moment, I don't want to put too much stress on him. This would have been a good time for a hospital tank, if I had any forethought (or money).

It is interesting how when I plug the air pump back in, almost immediately the dwarf cories stop pacing up and down the walls, and go right back to snuffling the sand. Does the amount of dissolved gases change that quick? Maybe it's just seeing the bubbles that somehow soothes them. I don't find the bubbles very soothing, myself.

Speaking of bubbles, I was thinking about why I don't see any gas bubbles in the mud layer, and now I think its probably just because the mud coats the glass, so I can't see the bubbles that are there, that's all.
 
anorth_uk said:
I'm looking at doing a FWDSB, but will be using a sump setup in lieu of the actual tank. Not sure yet if I'll go for a dark installation similar to marine DSB's of a lit version - may start off with it dark and see how that goes, can always add lights after
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If it's dark though, how will the plants grow? I think the plant roots are a pretty important part of the FWDSB's success. Freshwater doesn't have a whole lot of burrowing critters to keep the substrate aerated, so it needs the oxygen that the roots provide. Maybe if you really loaded it up with something that burrows, and nothing which might predate on the burrowers, that might work. Probably not as well as it does with plants, though. Hey, you could use the sump for breeding the inverts you feed to the fish in your main tank. What kind of substrate in the main tank? If you had a DSB and plants in the main tank, the sump wouldn't really be needed. I'm just thinking out loud, I hope I haven't said anything not nice. Good luck with your project!

Oh, and I took your advice about the snails, but I really messed it up. Instead of scooping them up in a cup, I used my net, thinking then the sand would sift back out, so I wouldn't have to seperate the sand and snails myself. Well the sand did fall out, and the snails stayed in nicely, but loads of blackworms were hopelessly tangled in the net, too! I felt so stupid. I had to try to squirt the worms out of the net with my turkey baster. The rainbows all crowded around, and whenever a worm blew out, they fought over who got to eat it. I eventually got almost all of the worms out, except one or two who got mushed into paste during the ordeal. Sorry, worms.
 
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I'll put MTS in to aerate the substrate and as they are nocternal it won't bother them, there's no point in trying a DSB in the main tank as cichlids will eat all the plant's except anubi and they dig too deep into the substrate. The main tank has sand (1st time I've used it, always had gravel before)

As most of the action I'm interested in (nitrate removal) happens underground the lack of light shouldn't be a problem

We don't seem to be able to get blackworms in the UK, unless I can find any in the bottom of my mom's pond (then will have to see if they can take the high Ph and temp)

Just working out the details of the sump, prob use a 18x12x12, 1st compartment would be a mechanical filter, 2nd the FWDSB, 3rd full of shells as a Ph buffer and 4th will contain the sump pump and heater - just need to get my grow-on tank cycled so I can move the fry from the proposed sump to the grow-on tank

For your snail problem go for one assassin snail, these need both sex's to breed and I haven't a clue how you sex a snail lol
 
anorth_uk said:
your snail problem go for one assassin snail, these need both sex's to breed and I haven't a clue how you sex a snail lol
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Candlight, wine, roses. Snails tend to be highly romantic creatures.

I can never resist that joke.
 
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?
 
Anoxia said:
Candlight, wine, roses. Snails tend to be highly romantic creatures.

I can never resist that joke.
Click to expand...

Wow! I wish someone would try that hard to figure out MY gender! Oh, to have the mystery and allure of the assassin snail!

Blackworms (Lumbriculous sp.) are native to N. America, Europe, and Asia. There are several species in the genus but they're virtually identical to one another. They prefer cool, unpolluted waters with nice detritus and mud to bury their heads in. Their tails stick out and resemble tubifex worms but tubifex tend toward more polluted, warmer waters and build little tubes which they stick out of. Tubifex may work as a substitute for blackworms, I'm not sure though. If they burrow deep enough to reach the upper anaerobic layer then yes. BUT they carry parasites and disease much more often than blackworms, I'm told.

Imagine a DSB with enough porosity (is that even the right term?) that the aerobic layer would be two or three inches deep. Then cichlids might play the role of gigantic, fast-acting mts! Plus, the openness of the bed to diffusion would allow H2S and so forth to diffuse upwards and be oxidized rapidly enough that rooted plants wouldn't really have a role to play in preventing supersaturation. I bet your DSB could be about 6-7 inches deep and be made from grains of .7 to 1.0 mm diameter. Maybe with finer grained sand below 3 inches from the surface. Cichlids as elements of the DSB, hmmm....

Nitrate removal is done by a wide range of bacteria but one group of autotrophic bacteria caught my attention - they oxidize H2S with the O from NO3 to derive the energy they need to extract the C from CO2 for use in chemosynthesis (like photosynthesis in plants but with chemical energy). These bacteria are sold as odor-reducing additives for outhouses and other sewage-y applications. They're non-pathogenic bacilli, harmless to fish, humans, and other varmints. Perhaps a sprinkle stirred into the DSB in the sump? http://www.biosafeone.com/index.html Might serve as a good example of what I suggest. It would enhance the DSB's ability to take in particles of solid waste and digest them away to nothing or almost.

I've been thinking about the O2/CO2 conundrum and yes, surely if the O2 level is low this is because the O2 is being consumed rapidly and therefore CO2 would be produced rapidly, assuming O2 is being absorbed from the air at a reasonable rate. If there is too much CO2, though, it doesn't mean too little O2, as CO2 is often formed anaerobically. IF we can come up with a way for you (Anoxia) to blow off CO2 from the tank without boosting oxygenation significantly, we could determine whether O2, CO2, or O2/CO2 are the problem.

  • (how to do this ?)
    blow off CO2 without adding O2 = happy fish; means too much CO2
    blow off CO2 without adding O2 = gasping fish; too little O2 or too little O2 and too much CO2
  • (circulation of the surface without agitation)
    add O2 without blowing off CO2 = happy fish; problem was too little O2
    add O2 without blowing off CO2 = gasping fish; too much CO2 or too little O2 and too much CO2
  • (air stone and air pump)
    Blow off CO2 and add O2 = happy fish; too much CO2, too little O2, or too much CO2 AND too little O2
    Blow off CO2 and add O2 = gasping fish; ??? check ammonia, nitrites, med or water conditioner overdose, ask local guru.

try 1., 2., and 3.
if the fish gasp for 1. and happy for 2. then the problem was O2
if the fish are happy for 1. they should gasp for 2. because there was too much CO2
if the fish gasp for 1. and gasp for 2. then the problem is CO2/O2

if the fish are happy for 1. and happy for 2. then something is wrong because you'll have added O2 and left CO2 the same to get happy fish and also have removed CO2 and left O2 the same to get happy fish - can't draw a conclusion from that.

if the fish are happy for 3. then any result other than 1.(happy) /2.(happy) is likely valid.
if the fish are gasping for 3. then the results of 1. and 2. are not valid and either you aren't successfully blowing off CO2 and leaving O2 or you aren't successfully adding O2 without driving off CO2 or both.

Is that crazy or what? I must've spent an hour and a half thinking that test up.
 
confusion said:
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?
Click to expand...

Circulation is carried out by partial pressures and lighter compounds rising in the substrate therefore sucking fresh material down, it is a bit mind blowing but it works :)
 
anorth_uk said:
Circulation is carried out by partial pressures and lighter compounds rising in the substrate therefore sucking fresh material down, it is a bit mind blowing but it works :)
Click to expand...

It's hard to imagine, but stranger things happen every day... But, that's the paradox... such circulation would also pull down dissolved O2, wouldn't it?
 
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