Deep sand bed and gasses

Ollie91

So I got into a debate on a facebook group that deep sand beds are bad because of the gasses they can release. From a bit of research ive found out that the nitrogen gas is harmless it's the rotten egg smell, (hydrogen sulphide) gas which kills off fish? So how do you make a deep sand bed that will consume nitrates and give off nitrogen gas without the Anaerobic gas being released too?


 

agsansoo

The only bacteria that will remove the nitrates is the anerobic bacteria, which only colonizes in the no-o2 or low-o2 areas. So how do you keep the septic tank (deep sand bed) from backing up ...? That's a great question.
1) Sand bed need to be at least 6" deep to promote anerobic bacteria.
2) Don't over feed.
3) Don't disturb the sand.

This is why I use a bare bottom.
 

matsungit

With the exception of neglected tanks I have never heard of any fish harmed by hydrogen sulfide from deep sand beds. Hydrogen sulfide is in gas form and just rises to the surface never to be seen again. Now it's different if for example you have a 5 year old deep sand bed and suddenly performed some thorough vacuuming. Everyone who keeps a deep sand bed knows that it shouldn't be disturbed and for good reason. There's so much unprocessed waste in there that if you disturb it, it will mix with the water and possibly poison your fish. It's like dredging a lake bottom. If you do it too much you may kill the fish population in there. But left undisturbed it's doing its job of filtering the water. This topic has been debated to death for years and up until now it's still a battle of theory and experience. It's your tank and you can do what you want and come up with your own conclusions.
 

junebug

Yeah, the key to a DSB is not to disturb it. Natural disruptions from fish and inverts, in the first inch or so of the sand, is usually fine, but below that you don't want and disruption.

Hydrogen sulfide is not harmful to the fish unless in MASSIVE quantities, dissolved in the water. What can be an issue is the bacteria that grow in these conditions, some of which are harmful. But, if you're not disturbing the sand, those bacteria won't be able to touch the fish. Not to mention if the fish are healthy, they're less likely to be affected by these bacteria.

In short, DSBs are great. They don't replace water changes, but do help with nitrate control, and when properly managed, will not hurt the fish. I realize this is the saltwater section, but I'll just throw it out there, I've been discussing DSBs at length with another member here and have been researching them pretty heavily, for use in a future freshwater tank (the process is exactly the same, as are the benefits). My 20 gallon long that I'll be using for native fish is going to have a DSB. They work best in low bioload tanks, so this is the best tank for me to try it in.
 

Ollie91

So basically don't disturb it and you're fine? Lol that's pretty much what I said and then a girl came along in the discussion and said she hadn't stirred her sand up for a few weeks and a big bubble of gas came out and wiped her tank out (we're talking freshwater at this point) so if I was to make a sump and leave a dsb alone in there it would be fine? And if any gass did come out it would go to the surface of the water and be released into the air?


 

matsungit

So basically don't disturb it and you're fine? Lol that's pretty much what I said and then a girl came along in the discussion and said she hadn't stirred her sand up for a few weeks and a big bubble of gas came out and wiped her tank out (we're talking freshwater at this point) so if I was to make a sump and leave a dsb alone in there it would be fine? And if any gass did come out it would go to the surface of the water and be released into the air?

Yes, that's basically it. Make it a long sump (the longer the better) and the sand bed 3-6" deep. Researchers have found that there are no apparent additional benefits if you make it deeper than 6" regardless of tank volume. The girl probably had old tank syndrome and blamed it on the DSB. Like how big of a bubble was she talking about? Golfball or pingpong size? That never happens on a typical well maintained tank. The biggest you should see is pea sized. And yes, the gas once released goes straight up into the air.
 

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