Does a DSB work the same in a fw as it does in a sw?

Sorry I haven't responded in some time but I have been busy.

As for the anerobes, isn't that what people shoot for with sw tanks? Thats why they have the DSB, so that it breaks down the nitrates. The clean up crew usually only gets to about the top inch or so of sand if that. Most of the clean up crew like hermits and snails really just get whats on top of the sand, in the nicks and crannies of rocks, and on the glass. So it's not like they're sifting through all three inches of the sand at one time (assuming the dsb is at least 3 inches). If this information is wrong then I guess my next question would be... why have a DSB if there is no purpose to a 'deep' sand bed? Your risking just as much in a sw tank if not more, that the anerobes will come up because of the clean up crew. Again it's just my understanding that the reason why people have a DSB is for the anerobes, otherwise why would you want them to set up and why would you have a DSB?

I'm just wondering if it works for salt water why wouldn't it work for fw. In the wild it's pretty much the same set up (excluding chemistry), water and sand for substrate.
 
As I said I have used a sand substrate ranging from 1in to 3in (approx) in places. I have had no problems with bad bacteria (but the tank hasnt been setup that long)

The main reason I went for sand is for looks, If your interested I have posted some pics up tonight.....

http://www.aquariacentral.com/forums/showthread.php?s=&threadid=31165

I have heard that you are just as much at risk in a tank with deep gravel as with sand of these bad bacteria
 
A) DSB in SW are the current trend, but they are by no means the only effective system for nitrate reduction. Most SW tanks have much more algal growths than a FW setup, which does a lot to reduce nitrates. There are many reports of DSB crashes--a large distrubance that releases the nasty by-products of the anaerobes (which, by the way is the threat--the bacteria themselves are harmless, since they typically die if exposed to a high oxygen environment. The by-products--ie, what's left after the bacteria consume the nitrate--can be various gases and chemicals that are toxic to fish).

However, there is no proof that DSB are beneficial in SW tanks, and a lot of people are pulling them out of their tanks. There is also a lot of discussion about the need for DSB (or porous liverock) in providing areas where anaerobic bacteria can develop. Anaerobes can develop in the shelter of biofilm--in other words, directly underneath a layer of aerobic bacteria. We know this happens--the bacteria that cause cavities in our teeth are anaerobic, and live under the healthy aerobic bacteria. So, it's possible that the anaerobes in SW systems are the same, and live under the protection of the aerobic bacteria. Why not the same in FW? Who knows? Maybe the anaerobic bacteria in FW tanks require something not provided in our tanks. Maybe the FW anaerobic bacteria are more sensitive to oxygen. Could be a variety of things.

B) I have 2 FW tanks that have sand in them, but have had many more in the past. Depth varied from less than one inch to about 2 inches. No biggers, many snails. I've never had any fish losses in these tanks. I tore one that had about 2 inches in it completely apart, and can vouch that the lower layers stank to high heaven--but I had played around with the tank several times, moving rocks, planting, etc, while the tank was still running and never saw any problems--but, these were rooted plants, also consuming nitrates and some of the other by-products, so I don't consider this tank an accurate test of a DSB that is unmaintained.
 
I have zero SW DSB experience, so cannot contribute there, but I have >15 tank-years FW plenum experience, so can make some comments.

The basic difference biologically between the plenums and DSB is the the plenum develops widespread anaerobic areas while avoiding full anoxia, which is highly likely in a DSB.

The original intent of the plenum was to avoid deep anoxia as required by the sulfur-reducing bacteria, but having sufficient anaerobic conditions to allow function of the nitrogen-reducing bacteria. The immediate micro-environment of both these and similar forms of bacteria are loaded with materials toxic to fish and inverts - nitite, ammonia, hydrogen sulfide, methane, all sorts of nasty things. BUT these materials will not diffuse up and out into the water column. If the bed (either plenum or DSB) is undisturbed, there are many bacteria at shallower levels (read as: higher oxygenation/redox levels) which will oxidize those materials as they diffuse upward. Nitrogen gas will dissolve and diffuse out to some extent from nitrogen-reduction areas, but much will bubble out as the gas - which is totally inert and harmless. IF the bed is severly disturbed (moving rocks, stirring) and it has H2S and such present in any quantity, you could have major issues - not definitely will, but could.

All this sounds fairly straight-forward, but to me it is difficult to have a long term tank without some substrate disturbance. My oldest individual plenum tanks are six +/- years old now, and all have had some disturbance. None have shown any signs of toxicity from that, nor any other symptoms of "sour" or overly organic substrates. I do not know if DSB could do the same, and have no plans to test such.

Personally I hate using sand in FW and will never do so again unless absolutely required (as for certain fish).

HTH
 
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Not to jump the thread, but RTR' have you written any articles on Plenums, I would be interested in much more info If I could get it ( more for curiosity and education than any other reason)

Also as to the previous discussion of MTS's keeping substrate mixed up, I think Lazersniper was on target with his comments. my understanding is that these snails will only go where there is oxygen ( seems pretty simple) so they won't dig into areas where you are likely to have an anerobic pocket. They won't go very deep at all except in substrate over a UGF plate and even then their depth of digging is arguable. My observation thus far is that MTS do'nt go far beyond the light. in most cases I can see the tail of their shells sticking out between gravel, and then when the lights go out they come out to feed.
 
There is a plenum article in the wings awaiting publication, likely late summer or fall.

Agree that MTS are limited by oxygen tension, so depth in any given substrate will be directly related to the O2 decrease curve in that substrate. The smaller the particle size and the greater the organic load, the faster the O2 levels drop with depth.
 
OK so heres what I pretty much gathered from this thread, just to recap.

1. Obviously we know that anerobic gasses are bad.
2. Deep sand beds are just a 'theory' right now and still show no proof of a certain benefit.
3. DSB are usable in either a FW or a SW tank as long as there are no 'great' disturbances done to the substrate enabling the escape of anerobic gasses.
4. Many people recamend using DSBs in SW tanks because it's the 'new trend'.
 
Well I don’t know what to say but I do have an inch of sand (for the cable hater) with about 1.5 inches of other gravel and stuff on top of it. This is how all of the books that talk about cable heaters tell you to do. I do find that I get some bubbles coming out of my gravel every day. I only vacuum / stir the top 1/4” or so of my gravel so the root tabs will not change my water chemistry to much.

I keep thinking that the DSB’s work like a Denitrificatio Chamber. This is only a thought of a PEE BRAIN.
- The ammonia eating bacteria is on the upper layers of the sand.
- As it goes down the nitrite eating bacteria.
- And you guessed it it’s time for the nitrate eating bacteria.
- If the flow of water is very slow and not a lot of oxygen at this point you could get some bacteria to change the nitrates in to nitrogen gas.

I do think that with the deeper substrates in tanks I can be bad to stir too much of the substrate at a time. It will release a lot of smelly stuff and will change balance of the bacteria.
 
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