Creating a safe anoxic environment.

[sammander]

Over the past few months I have come across information regarding the creation of anoxic environments in aquariums, one of them being a deep sand bed (around 10+ cm?). I have also heard that some people worry that it could create hydrogen sulfide, which could creep out if the sand bed is disturbed too much and kill everything (though this could be neutralised with enough oxygen in the water, maybe with bubble stones?).

Could one for example, create a base layer of the Marine Pure blocks (maybe too brittle) or Xport-Bio dimpled bricks and then even put a small layer of sand over these (if you want the sand of course). I know this is probably very expensive, but could that actually work?

Please let's assume everything is happening inside the tank so no sumps, hobs, canister filters etc.

Am I just crazy and misunderstanding something?

 

[DrTim]

Why do you want to create an anoxic layer?

 

[sammander]

Why do you want to create an anoxic layer?

As one method of nitrate removal.

 

[DrTim]

If you would allow me

You cannot reduce nitrate in an anoxic zone.
Denitrification happens in anaerobic zones.

This is commonly confused even by many manufacturers/seller of bacteria products.

The only thing that will be produced, as you noted, in an anoxic zone is hydrogen sulfide (HS). Even in the presence of oxygen HS will kill your fish, corals AND bacteria because it is much, much more soluble in water than oxygen.

At 25 C the solubility of oxygen is about 0.04 gram per kg of water
At 25 C the solubility of hydrogen sulfide is 3.5 grams per kg of water

So bubbling is not going to help much. There are engineering calculations available that would tell you how much energy you would have to have in the water to neutralize the hydrogen sulfide - it's a lot!

As the chart shows below the redox value (and so the oxygen concentration more or less) determines what microbial activities can occur.

The issue is always that you cannot easily control the set-up and keep it anaerobic versus anoxic.

I would contend there is no such thing as a 'safe' anoxic environment in an aquarium. The hydrogen sulfide will get you sooner or later.



Regards

 

[LotsOreefs]

If you would allow me

You cannot reduce nitrate in an anoxic zone.
Denitrification happens in anaerobic zones.

This is commonly confused even by many manufacturers/seller of bacteria products.

The only thing that will be produced, as you noted, in an anoxic zone is hydrogen sulfide (HS). Even in the presence of oxygen HS will kill your fish, corals AND bacteria because it is much, much more soluble in water than oxygen.

At 25 C the solubility of oxygen is about 0.04 gram per kg of water
At 25 C the solubility of hydrogen sulfide is 3.5 grams per kg of water

So bubbling is not going to help much. There are engineering calculations available that would tell you how much energy you would have to have in the water to neutralize the hydrogen sulfide - it's a lot!

As the chart shows below the redox value (and so the oxygen concentration more or less) determines what microbial activities can occur.

The issue is always that you cannot easily control the set-up and keep it anaerobic versus anoxic.

I would contend there is no such thing as a 'safe' anoxic environment in an aquarium. The hydrogen sulfide will get you sooner or later.



Regards

Could you explain the chart a little bit by chance? I’m afraid it doesn’t look much like English to some of us....well at least myself.

 

[sammander]

This is great. Thank you for the clarification on what I stated, yes I was incorrect, denitrification occurs, so nitrates eventually break down into nitrogen gas yes? So it seems the only way to possibly do something like this successfully is to have a very highly controlled and stable environment with specialised equipment that would actively make adjustments to offset the HS?

Since we do get anoxic environments deep with our rock structures, are they safer because these cannot be as easily disrupted like a deep sand bed can? Am I correct in understanding that stirring up deep sand bed would release too much SH at one time thus creating the toxic environment? But there are benefits to creating natural environments that do denitrification for us yes? If so, would having a deep "rock bed" provide a similar situation without the fear of releasing too much SH at one time while at the same time providing more room for biological filtration?

If this is the case, would my theory of lining the entire floor of my aquarium (though expensive) with these blocks be a benefit? Maybe if not for denitrification then I guess they would only increase biological filtration?

 

[RocketEngineer]

I think you have a misconception. We really don’t get anoxic environments anywhere in our tanks. There is simply too much flow. This drives oxygen into the deepest crevices and right to the bottom of most sand beds.

Now, I have created an anaerobic zone outside my aquarium that dropped my nitrates significantly. This was accomplished using a 5g bucket almost totally full of sand with a flow of water across the top. Years later, I shut it down and the sand was just fine, no rotten egg smell at all. Simple biology, purpose built environment, no technology needed.

 

[Randy Holmes-Farley]

I'm not sure how this concept is substantially different than deep sand.

I had deep fine aragonite sand in a refugium for years. In the end, i saw no apparent benefit or detriment to it, and tossed it.

 

[DrTim]

I think you have a misconception. We really don’t get anoxic environments anywhere in our tanks. There is simply too much flow. This drives oxygen into the deepest crevices and right to the bottom of most sand beds.

Now, I have created an anaerobic zone outside my aquarium that dropped my nitrates significantly. This was accomplished using a 5g bucket almost totally full of sand with a flow of water across the top. Years later, I shut it down and the sand was just fine, no rotten egg smell at all. Simple biology, purpose built environment, no technology needed.

I would disagree - I talk to a lot hobbyists at all the shows and over the years I have spoken to several (usually with deep sand beds) that wiped their entire tank out by disturbing the sand, releasing HS and killing everything. Is it common no but it happens.

 

[brandon429]

the ones from remote buckets are lacking rock stacks, powerheads that dislodge, and burrowing fish (current is pass-through back to main tank, can be taken offline if req'd)

one would nearly have to stick an arm in on purpose to disrupt, however power outage planning for that mix of generalized aerobes/02 sink for the most part needs to be in check

I would be more concerned of the in-tank reducing bed attempts where disturbance happens by accident. can't even clean rocks or remove them without clouding up in-tank sandbeds.

the threads on whether or not those kill tanks goes on for twenty pages as usual, variation abounds with in-tank DSB's and the remote bucket ones are pretty streamlined regarding safety.

for sure all our work in the sand rinse threads is dealing with variation of in-tank sandbeds. they have problems more often than they don't based on work threads we do setting up tanks in forums and tracking them over months/yrs. But in the big debate threads its nearly split down the middle with longstanding DSB's claiming safety and then a portion stating how that disturbance mentioned did wipe their tank...

I have yet to recall a bare bottom setup losing fish and corals to ammonia events.

 

[sammander]

Ok so again my question is because I feel it wasn't actually answered. If this is the case, would my theory of lining the entire floor of my aquarium (though expensive) with these blocks be a benefit? Maybe if not for denitrification then I guess they would only increase biological filtration? These stones would not be able to be stirred up to release anything dangerous into the tank. They also have a lot of surface area so I would have a huge biological filter at the very least and if there are anoxic zones created, cool if not oh well.

 

[brandon429]

you'll have to measure it and report back. even people who do show denitrification in system A can't set up ten more systems and earn denitrification, its a unicorn. its harmless for you to try the setup though

if you sampled 100 deep sand beds running, 90 of them produce nitrate vs gas it off.


even the tests we use to discern if denitrification is occurring, range so wildly in name brand comparison threads Im not sure that all of the claimed 0 nitrate systems are that way. simply measuring nitrate accurately is a total challenge, we are horseshoeing most measures in reefing except for when a working seneye shows what ammonia does-that's reliable.

 

[sammander]

Ok thanks.

 

[brian414899]

If you would allow me

You cannot reduce nitrate in an anoxic zone.
Denitrification happens in anaerobic zones.

This is commonly confused even by many manufacturers/seller of bacteria products.

The only thing that will be produced, as you noted, in an anoxic zone is hydrogen sulfide (HS). Even in the presence of oxygen HS will kill your fish, corals AND bacteria because it is much, much more soluble in water than oxygen.

At 25 C the solubility of oxygen is about 0.04 gram per kg of water
At 25 C the solubility of hydrogen sulfide is 3.5 grams per kg of water

So bubbling is not going to help much. There are engineering calculations available that would tell you how much energy you would have to have in the water to neutralize the hydrogen sulfide - it's a lot!

As the chart shows below the redox value (and so the oxygen concentration more or less) determines what microbial activities can occur.

The issue is always that you cannot easily control the set-up and keep it anaerobic versus anoxic.

I would contend there is no such thing as a 'safe' anoxic environment in an aquarium. The hydrogen sulfide will get you sooner or later.



Regards

The definition of anaerobic is no free available D.O or dissolved oxygen and no chemically bond oxygen such as nitrite or nitrate or even Po4 for that matter....

 

[brian414899]

The definition of anaerobic is no free available D.O or dissolved oxygen and no chemically bond oxygen such as nitrite or nitrate or even Po4 for that matter....

Anoxic is no free dissolved oxygen but still has chemically bond oxygen such as nitrates

 

[Bob Escher]

I would disagree - I talk to a lot hobbyists at all the shows and over the years I have spoken to several (usually with deep sand beds) that wiped their entire tank out by disturbing the sand, releasing HS and killing everything. Is it common no but it happens.

i stir parts of my tank a little at a time, so I may do 1/4 of at at one time just before I do a water change. So at every water change I do a little by little