Anoxic denitrification in canister filters?

[BlubAquatics]

So, I got into a discussion with someone about overstocking tanks (e.g. 10 fancy goldfish in a 3ft tank) and my stance was that it would be inhumane due to space and water quality concerns. 

But there was this guy who claimed that it's perfectly fine because "as long as you have enough filtration you can achieve 0 nitrates". He shares his experience with his "3 ft tank with numerous small tetras, corydoras, altum, discus, plecos that has 0 nitrates" with 2 Eheim Classic 350 filters with 3-4kh of biohome media.

Sensing something amiss, I enquired further and it turns out that that he has peace lilies growing out of his tank as well, which I think would be the one responsible for 0 nitrates. 

If anyone is interested in what the guy said exactly, click here.

So, my question is: Can one reasonably achieve adequate denitrification using canister filters to bring nitrates down to 0? 

[Flumpweesel]

The longest I got with two comets in a 60G (240l) with a canister (fluval 306 and a Hagen Stingray 15 for extra flow) was about a month. No plants though which would have probably got me further.

Goldfish and plants don't easily mix though. 

I wouldn't say it would be impossible to balance three tank in question but I wouldn't want to try it myself.

It will be pretty crowded when they grow out though 

[face]

IMO no denitrification is really no practical in a freshwater aquarium especially in a canister

to start with denitrification requires no dissolved oxygen canisters pump oxygenated water through them at a relatively high rate really not a good place for denitrification some filter media clams  to have anaerobic areas but the amount of area thats anaerobic would be very small

for example in a saltwater aquarium they normally use 1 pound per gallon of reef rock which acts just like filter media and even that  isn't enough area to get 0 nitrate for most people with very light stocks tanks by freshwater standards (and all the corals and algae)

for a more practical idea i remember a guy that built a denitrification filter for his 125 it was a 12 foot tall 6 inch round pvc pipe filled with matrix filter media and a tiny pump to get water into it and it still wasn't enough (he also had to carbon dose since his tank was carbon limited)

that said automatic water changes plants refugiums algae scrubbers and maybe even denitrification can keep nitrate in check but there is a lot of other things to worry about when stocking an aquarium nitrate is just the simplest thing to point to you can just look at places that breed feeder fish to see what kind of stockings are possible.

[modified lung]

There's too much flow through a canister filter for denitrifying bacteria to survive. Plants like pothos, lucky bamboo, and I'm sure peace lilly suck up nitrate like crazy though.

[Wrencher_Scott]

On 8/7/2022 at 9:13 AM, BlubAquatics said:

So, I got into a discussion with someone about overstocking tanks (e.g. 10 fancy goldfish in a 3ft tank) and my stance was that it would be inhumane due to space and water quality concerns. 

But there was this guy who claimed that it's perfectly fine because "as long as you have enough filtration you can achieve 0 nitrates". He shares his experience with his "3 ft tank with numerous small tetras, corydoras, altum, discus, plecos that has 0 nitrates" with 2 Eheim Classic 350 filters with 3-4kh of biohome media.

Sensing something amiss, I enquired further and it turns out that that he has peace lilies growing out of his tank as well, which I think would be the one responsible for 0 nitrates. 

If anyone is interested in what the guy said exactly, click here.

So, my question is: Can one reasonably achieve adequate denitrification using canister filters to bring nitrates down to 0? 

Impossible. Like @face said, you need no oxygen, and that will not happen. 

I believe you are correct in that was the plants that did the trick. 

A few big fish put out a lot more waste than lots of small ones.

As for  space that is highly debatable and up to the owner, as for water quality all you need is lots of biofiltration and enough water changes to keep the nitrate at a reasonable level. 

How big do they get? 6" or so? That doesn't sound to bad to me. 

It's kind of funny, I have a 4 foot long tall style tank (90 gallons) and 6 Discus and a few other smaller fish. I swear I could cut my tank in half because they always hang out on one side anyway. I have never seen them swim laps like Michael Phelps enjoying the large tank. 🙂

Anyway, I would get the largest canister you can afford and fill it with coarse foam like 20 or 30 ppi and go for it. A big filter on that tank filled with good media like foam will keep that water clean.

[Guppysnail]

On 8/7/2022 at 12:13 PM, BlubAquatics said:

Can one reasonably achieve adequate denitrification using canister filters to bring nitrates down to 0? 

No. This thread explains testing the actual capabilities  and the astronomical volumes of anoxic bacteria needed to accomplish this with media.  I have peace lilies in 5 tanks. I can tell you they will strip a tank that’s not overstocked and overfeed of nitrate quick. 

 

[asondhi]

I have heard rumor that large enough lava rock (undrilled) and significant lava rock gravel mounds under the sand/other substrate can house a reasonable mount of anoxic bacteria and can potentially contribute to denitrification... I wish I had a specific source for this but would love to hear if anuone has heard the same

[face]

On 8/7/2022 at 6:06 PM, asondhi said:

I have heard rumor that large enough lava rock (undrilled) and significant lava rock gravel mounds under the sand/other substrate can house a reasonable mount of anoxic bacteria and can potentially contribute to denitrification... I wish I had a specific source for this but would love to hear if anuone has heard the same

it should work similar to reef rock in saltwater it would require a lot to be effective you also have to get water to it if its underneath substrate its geting no flow its fickle to much flow and it doesn't work to little and well it can't filter water it doesn't touch.

[BlubAquatics]

Thank you everyone for confirming what I suspected. I do have a bachelors in Biological Sciences so I could pick up all the bullshit that guy was spouting, but just had to confirm it with the experts.