Deep Sand Bed Problems

[AChap]

When disturbing substrate there are a couple of things that can happen. One is indeed toxins like hydrogen sulphide being released at once. When into the water column, it pretty much evaporates/ makes a reaction and is neutralized but on it's way out of the water it may affect fish if you released too much at once and fish were in the way. However, it's more harmful when bottom feeders dig into the substrate rather than anything else.

The other issue is an ammonia spike which normally follows when one disturbs the substrate way too much. In both cases when you do that, you need to follow with a large water change or two. Then it should be pretty much safe for the fish. This is more likely the reason your fish died? Have you measured the ammonia/nitrites?

And why having a deep sand bed?

Siphoning a deep sand bed will not prevent either of these issues happening in the future. Sand compacts back within minutes. When the substrate is deep, it doesn't get enough oxygen into the bottom layers and anaerobic decomposition occurs. Anaerobic decomposition causes the production of harmful gasses such as hydrogen sulphide and others. It stays in there if you don't touch it, but once you disturb it, all this can go out at once.

If you have a thin layer of substrate, then because it gets oxygen, aerobic decomposition occurs instead, which produces CO2 instead and not hydrogen sulphide or at least not in high amounts. The CO2 as you know pretty much goes straight out via the surface agitation and doesn't harm the fish.

Both processes also produce ammonia. Disturb any substrate, it goes out into the water column. Siphoning can reduce the amount of organics those bacteria use to produce ammonia and gasses but to be honest it's impossible not to have organics in the substrate. Siphoning only helps to keep the substrate aerobic to an extent as it doesn't get clogged to the point of oxygen not reaching there.
And this sort of setup where one has "oxygenated" substrate is healthier for at least bottom feeders as it also doesn't promote harmful bacteria that may directly affect fish.

Best way to get nitrates out of the water is water changes and not a deep sand bed in which what happens one can't control.

My first time replying with my newly created MFK page. I only wish I had read this sooner. Took my 11 inch albino Oscar and some Mbunas into the store for credit. They just did not seem to be thriving in my 55 gallon. I really think it was the substrate! I put a couple of Flowerhorns in that tank on Tuesday and they too don't seem to be thriving. Can I clean the sand with them inside or should I just take it all out? Thanks I'm new.

 

[Coryloach]

If you think it's the sand and you want to leave the fish in, do it in patches carefully and don't let the dirt into the water column. Siphon some of the sand while doing so. Make sure that's accompanied by a water change. The extra water changes would do the tank good to improve water quality too. You may get a diatom outbreak as well if you overdo it at once(that's because of the ammonia).

Take in it out all at once can sometimes cause an ammonia spike as well, because there could be enough nitrifying bacteria established in the substrate that plays part of the overall balance.

 

[duanes]

I find if you have a deep sand bed, you need to keep small burrowing animals such as crustaceans and molluscs that reside in the substrate to keep it from going anaerobic.
Even with a plenum underneath.
This is less difficult in a marine tank, because there are so many options.
In freshwater I use Malay live bearing snails, and gammarus shrimp. I realize MTS snails are a scourge to some, because they can plug lines and filters, and at times unsightly.
But I find their constant rummaging through the sand keeps it from compacting, and they also help break down detritus, making the byproducts more easily available for bacterial usage.
This does not mean vacuuming the substrate can be neglected though, I still do vacuum weekly making sure no H2S pockets build up.

Gammarus (AKA scuds) they also make great snack for large enough fish

 

[ragin_cajun]

how deep are we talking about here when we talk about a "deep sand bed"?

 

[tlindsey]

I have a 55 gal... Setup with sand ss substrate, and at one time there were Geo's in it that would sift through the sand and would create some deep sand areas, so what what I use is a hanger twisted one end to a small loop. Before I siphon any water out I stick the hanger in the sand, and drag it through slowly, so far have not had any sulphur pockets develope

 

[AChap]

If you think it's the sand and you want to leave the fish in, do it in patches carefully and don't let the dirt into the water column. Siphon some of the sand while doing so. Make sure that's accompanied by a water change. The extra water changes would do the tank good to improve water quality too. You may get a diatom outbreak as well if you overdo it at once(that's because of the ammonia).

Take in it out all at once can sometimes cause an ammonia spike as well, because there could be enough nitrifying bacteria established in the substrate that plays part of the overall balance.

Thanks I put sand in all my tanks without doing any research. Almost makes me want to go back to gravel.

 

[xraycer]

Thanks I put sand in all my tanks without doing any research. Almost makes me want to go back to gravel.

I've switched to sand(PFS) 3 years ago....never going back to gravel