Originally Posted by lmetcalf
I understand that aerobic bacteria break down the ammonia into nitrate, (nitrogen cycle) but what about anaerobic? (ammonia into nitrogen gas)
Ive heard mixed opinions about whether anaerobic bacteria is ok (therefore go with deep substrate)
Stop the growth of anaerobic bacteria and only have aerobic bacteria (shallow substrate)
Im not sure if this anaerobic bacteria sounds like a good thing.. is this the "bad bacteria" that everyone talks about?
Ahhh... the "how deep of a sand bed" question. I think of ALL the things I researched when I started my tank, THIS was the most confusing one of all because of all the conflicting information/myths/conjecture out there. So I'm here to say... I think little bits of everything you've read is correct - but I don't know what bits those are. Here's my take of the whole thing...
From the majority of info out there, you don't really have a DSB
unless you have more than 4" of sand. 6" is a better goal. The real gray are is between 3" and 4" - this is the no man's land where you don't have enough depth for anaerobic bacteria, but you have too much depth to keep a clean sand bed without disturbing the lower layers and causing issues.
With that said... my sand bed is between 3 and 4 inches! Go figure. I started out with 4", but just couldn't bring myself to add more. And as the critters moved sand around on me, and I've sucked some out over the years, I'd say my average depth is 3.5". Have I witnessed devastating effects? Nope. Over the 3 years my tank has been running, my nitrates have rarely gone above 2.0ppm, and everything is thriving. I can't say that it's due to my semi-deep sand bed, but it's sure not hurthing anything either.
Yes... DSBs can generate the infamous and dreaded "H2S" or hydrogen sulfide gas. Many things I've read makes it sound like the H2S builds up this huge bubble in your sand bed that will someday rise to the surface and kill your entire tank, fill your house with the smell of rotten eggs, and cause your entire neighborhood to be evacuated. I'm not doubting that a DSB
(or any sand bed for that matter) can develop H2S, but my opinion is that what little gas builds up filters through your sand bed and bleeds off in small amounts that most likely are never noticed by the livestock. Again... just my opinion.
And just so we get things straight - aerobic bacteria is the stuff that lives on your rocks, sand, filters, etc. that turn the ammonia into nitrites, and the nitrites into nitrates. Anaerobic bacteria is the stuff that then turns the nitrates into nitrogen gas, which then escapes your tank in bubbles. All properly cycled SW
tanks will have aerobic bacteria. Some SW
tanks, depending on the filtration will have anaerobic bacteria. Both bacteria are "good". I'm not aware of any "bad" bacteria when it comes to biological filtration.
Yeah... the whole DSB
issue is tough to digest. In hindsight, I stressed too much about it. If what you decide to go with doesn't work for you, then change it. Nothing we do is set in stone... or sand.
[Edit: Oh... and welcome to Aquarium Advice!]