Where Exactly Is The Bacteria At?

[nmonks]

Good question. Never seen this either, and I've used sandy substrates in tanks for over ten years. Certainly, I've seen gas bubbles, and I've also smelled bad smells from old sand beds while cleaning them. Has this ever harmed the fish? No. My guess is you need quite a lot of gas and/or minimal water movement for it to be an issue. Possibly in the "old days" of the hobby it was a risk, but with modern filters turning over the water so quickly, the risk is probably very small to zero.

Cheers, Neale

Many people warn of the dangers of fatally toxic gasses building up if a sand bed in FW is deeper than an inch or two, however by having a deep sand bed (6" or so) one can culture bacteria to aid in nitrate export. Now I have seen tests which show that nitrate is consumed in tanks with DSB, but never seen any first hand stories of deaths from large sand beds.

 

[Bignose]

The dangerous gas that builds up from anaerobic bacteria is hydrogen sulfate. Hydrogen sulfate is indeed one of the deadliest substances on earth. However, the really good news is that in the presence of oxygenated water, hydrogen sulfate is very, very quickly converted into something else. The news is really good for fishkeepers, since you know the water was well-oxygenated or else the fish would be suffocating. So, unless there was an exceptionally large bubble of hydrogen sulfate, the water istelf neutralizes the threat.