Deep sand bed and Anaerobic bacteria

[giar]

Hi folks,

I heard some good stories and bad stories about DSB and Anaerobic bacteria.

And now I wanna have a 20cm thick sand bed to my 6,600 gal tank.

So my questions are :
1- what do i really need to pay attention with anaerobic bacteria in deep sand bed so it wont kill my fish

2- why i heard so many horror stories with anaerobic bacteria. What would the cause that make people freak out with anaerobic bacteria?

3- please share your experiences with deep sand bed

Thx

 

[twentyleagues]

You are going to get all kinds of stories. The issue with dsb is that it is a low oxygen zone which is great for anaerobic bacteria. Anaerobic bacteria are a good thing they break down nitrates. There are only a couple ways to get rid if nitrates in our tanks and thats water changes, plants, or anaerobic bacteria. The first two are easy. Anaerobic bacteria needs special conditions to exist and are slow to grow. There are plenty of people who use anaerobic filters to remove nitrates in their systems. I think personal horror stories of huge gas pockets killing all life in the tank are mostly incorrect assumptions of the reason why their fish died. Its more likely bad maintenance in the first place. Hydrogen and sulfer gasses can be created in a dsb. You've got to make sure not to disturb the lower regions of the sand and to not introduce anything organic in the deeper portions as this is what causes gas pockets. Its like if you dont normally eat beans and all of the sudden you decide beans sound like the best food ever. Your system can break it down and use it but its got some extra stuff it creates in the process. That's what anaerobic bacteria do with things they are not used to breaking down. They can consume them like normal bacteria but it creates unwanted byproducts.

When I had saltwater I had a 90g standard which was half full of sand as a deep sand bed tied into the system. With hundreds of corals and fish in the same system I did water changes every two weeks and my nitrates never went over 15ppm. I basically did water changes to replenish trace nutrients. That was setup for at least 7 years, it also housed my nps corals. When I broke the system down that sand smelled terrible but I never had a system ending gas bubble. Only the top inch or two ever got disturbed. No fish were present in that tank as I worried that the rhizos may eat a fish if it ventured to close. Which is why the nps corals went there in the first place.

I know this isn't the most scientific telling of dsb activity, but I hope it helps. Currently I am or have been working on an anaerobic or as they say anoxic filter for my fresh water system but have had little success. There is alot of dosing to get it right. And I did use biopellets in saltwater which helps to produce anaerobic bacteria also. I also did some vodka dosing (tank and self sometimes ) to help the bacteria out. I've tried these methods in fresh water and havent really seen the same nitrate reduction that I saw in saltwater. Current plans are on hold for the time being but experimentation will continue shortly.

 

[Backfromthedead]

True that anaerobic bateria will absorb some nitrates, but it is a double edged sword in my opinion since large colonies of these bacteria produce large amounts of toxic byproducts such as hydrogen sulphide when they process said nitrates. In a closed system of small volume like our aquariums, it is too volatile to try and actually maintain these bacteria which is why im a substrate minimalist myself.

 

[Hendre]

Agreed with the above. In an anaerobic filter the gases leave the system slowly as they are constantly released but in a deep sand bed the gas can saturate the substrate until it either bursts forth or is disturbed, potentially killing many fish in the process. IMO a waterchange is much easier... It works in nature due to HUGE volume, low concentration of fish..

 

[duanes]

Unless you have lots of plants, and a crew of animals like Malayan cone snails that live in the substrate, and constantly work it, moving it around to keep the bed anoxic (as opposed to becoming anaerobic) pockets of hydrogen sulfide can build up, so care should be taken. Anaerobic areas occasionally burp rotten egg smelling gas bubbles, and H2S04 can sometimes build to toxic levels in the tank.

Back in the 80s, plenums were a thing (especially on salt water tanks, where water changes are expensive). Plenums are an area constructed, creating a zone of anoxic water under the sand. Google Bob Goemans Plenum method for nitrate removal/redux potential.
I tried them, but because I keep cichlids they always dug in, negating the redux process.

I have tank, with some deep sand areas now, these are crammed with plants, and there are lots of burrowing critters, and yet I, occasionally get H2SO4 burps, but because the tank is outside, those burps are less like a giant Jaba the Hut mega fart, that if allowed to burp a house inside could easily gas people out.