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Anoxic denitrification in canister filters?

corymbosa

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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?
 

dw1305

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Hi all,
Can one reasonably achieve adequate denitrification using canister filters to bring nitrates down to 0?
No, and if you could? It would be a <"ludicrous idea">.

I really don't understand why it <"continually pops up"> as a tenable argument. Nitrate (NO3-) isn't toxic until <"you reach very high levels">, but <"ammonia (NH3) and nitrite are toxic"> at below 1 ppm (mg / L).

Why would you want to risk your livestock by building a system that was always teetering on the brink of a <"positive feedback tsunami of toxic ammonia">?
cheers Darrel
 

sparkyweasel

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Zero nitrate is not a useful goal.
Happy and healthy fish is a better goal to aim for.
Fish like space to swim around, the choice of interacting with their tankmates or keeping away from them, and a rich environment to live in. No amount of filtration will add that to a tank that is too small.
 

_Maq_

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Can one reasonably achieve adequate denitrification using canister filters to bring nitrates down to 0?
I believe denitrification quite often occurs in our tanks. But not within canister filters, rather in deeper (suboxic) zone of the substrate.
I also believe that it's not a viable way of getting rid of nitrates, especially not in an overstocked tank.
And like @sparkyweasel said, I'd stress it even further: Those people who keep excess fish in tiny tanks should better quit tank-keeping altogether. It's a sure sign they are completely insensitive to living creatures. To hell with such people.
 

dw1305

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Hi all,
Zero nitrate is not a useful goal.
No <"definitely not">, the other point would be that I very much doubt that those people reporting "zero N03" really <"have no nitrate">.
I believe denitrification quite often occurs in our tanks. ....... rather in deeper (suboxic) zone of the substrate.
Same for me, I want <"natural processes"> to occur in <"the substrate">. This what Stephan Tanner has to say <"Aquarium biofiltration">. I'm much keener on <"Dr Tanner"> (<"and Dr Seuss">) than Dr Novak.
But not within canister filters, rather in deeper (suboxic) zone of the substrate.
It is the sealed nature of the canister filter that makes anaerobic denitrification such a dangerous concept. A <"finite amount of oxygen"> enters the filter, and if the Biochemical Oxygen Demand (BOD) <"exceeds that dissolved oxygen supply"> you run the real risk of ammonia levels building up.

You can mitigate for any potential build up of <"fixed nitrogen"> by having a <"back-up ammonia removal system">, ideally <"plant based">.

cheers Darrel
 

_Maq_

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you run the real risk of ammonia levels building up
Do you think DNRA (dissimilatory nitrate reduction to ammonia) occurs in our tanks or in canister filters? I'm more concerned about sulfate reduction to sulfide - H2S, HS- - or incomplete degradation of sulfur containing organic compounds - organosulfides. Unlike ammonium, these are toxic to all organisms, incl. plants.
Anyway, I agree that rarely cleaned canister filters ("to let bacteria proliferate") present a potential risk.
 

dw1305

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Hi all,
Do you think DNRA (dissimilatory nitrate reduction to ammonia) occurs in our tanks or in canister filters?
Unfortunately <"I don't know">. I'd guess that it isn't important in planted tanks, but we are back into <"unknown unknowns"> territory.

I think you could definitely "design" <"a system where it occurs">, if you had a lot of very carbon rich material in a deep substrate with limited permeability. This is the schematic from a <"Winogradsky column">, showing the full sequence of electron acceptors.

fig5702p56a-jpg.92634

I'm more concerned about sulfate reduction to sulfide - H2S, HS- - or incomplete degradation of sulfur containing organic compounds - organosulfides. Unlike ammonium, these are toxic to all organisms, incl. plants.
If you look at plants like mangroves (<"Rhizophora mangle">* etc), that occur in potentially sulphate reducing conditions, they have physiological and morphological adaptations to avoid anoxia. I believe we both use silica sand based substrates, with very little oxidisable material in them, partially to avoid potentially large oxygen deficits within the substrate.

That is partially why I would really like <"an emergent plant rooted into the substrate">. Ideally something like a <"Cyperus"> or <"Nelumbo species">, with very efficient aerenchyma.

* If that link stops working the reference is: "Potential for Sulfate Reduction in Mangrove Forest Soils: Comparison between Two Dominant Species of the Americas".

cheers Darrel
 

corymbosa

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Hi all,

No, and if you could? It would be a <"ludicrous idea">.

I really don't understand why it <"continually pops up"> as a tenable argument. Nitrate (NO3-) isn't toxic until <"you reach very high levels">, but <"ammonia (NH3) and nitrite are toxic"> at below 1 ppm (mg / L).

Why would you want to risk your livestock by building a system that was always teetering on the brink of a <"positive feedback tsunami of toxic ammonia">?
cheers Darrel
Hi Darrel,

Regarding nitrate levels, could you review these two papers and see if they are any different from the papers you have cited in your links?

This paper suggests that High nitrate nitrogen (80–100 mg/L) was related to chronic health and welfare impacts to juvenile rainbow trout.

And this paper found significant effects of nitrate as low as 125ppm on biomass yield, length, weight and specific growth rate (SGR) of turbot.
 

dw1305

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Hi all,
Regarding nitrate levels, could you review these two papers and see if they are any different from the papers you have cited in your links?
It is a <"fair question"> and I'll say straight away that, personally, I have low nutrient tanks and that includes <"low nitrate levels">.

The problem is untangling if the nitrate (NO3) is the <"smoking gun"> of higher levels of ammonia (NH3) and nitrite (NO2) or it was added from a salt like potassium nitrate (KNO3).

The Danio rerio paper added NO3 via <"sodium nitrate (NaNO3)">.

cheers Darrel
 

ElleDee

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The problem is untangling if the nitrate (NO3) is the <"smoking gun"> of higher levels of ammonia (NH3) and nitrite (NO2) or it was added from a salt like potassium nitrate (KNO3).
Over at TPT it was often said that higher nitrate levels from fertilizer is not equivalent to nitrate levels from fish waste and other natural processes in the tank. Not because the nitrate itself is different, of course the ions are exactly the same, but because nitrate levels that naturally accumulate are a proxy for other waste products that are accumulating as well. I haven't read any research supporting that idea, but that sounds very reasonable to me.
 

corymbosa

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Hi all,

It is a <"fair question"> and I'll say straight away that, personally, I have low nutrient tanks and that includes <"low nitrate levels">.

The problem is untangling if the nitrate (NO3) is the <"smoking gun"> of higher levels of ammonia (NH3) and nitrite (NO2) or it was added from a salt like potassium nitrate (KNO3).

The Danio rerio paper added NO3 via <"sodium nitrate (NaNO3)">.

cheers Darrel
So if I understand correctly, high nitrate levels are more concerning if they came from the oxidation of ammonia from fish waste, because the high initial amount of ammonia and nitrite will be way more dangerous to fish.

But, what if the high nitrate concentration was accumulated over a long period of time from relatively low and safe levels of ammonia?
 

dw1305

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Hi all,
Over at TPT it was often said that higher nitrate levels from fertilizer is not equivalent to nitrate levels from fish waste and other natural processes in the tank. Not because the nitrate itself is different, of course the ions are exactly the same, but because nitrate levels that naturally accumulate are a proxy for other waste products that are accumulating as well. I haven't read any research supporting that idea
I think that is the question that the "Zebra (Danio) fish" (Danio rerio) papers try to answer. Have a look at: Pereira, A., et al (2017) <"Histopathological changes and zootechnical performance in juvenile zebrafish (Danio rerio) under chronic exposure to nitrate">, Aquaculture, 473.
For that, groups of 30-day-old zebrafish were exposed to < 7 (control), 100, 200, and 400 mg L− 1 nitrate-N for 28 days. No mortality was registered in fish exposed up to 200 mg L− 1 nitrate, and all individuals seemed externally healthy; however, in fish exposed to the highest nitrate concentration mortality reached 47% at the end of the trial, and many individuals showed lethargy, abnormal swimming, emaciation, lordosis, and/or superficial lesions. Although final growth was not significantly different among groups, growth parameters tend to decrease with increasing levels of nitrate, and a significant negative correlation was found between weight gain and nitrate levels, suggesting a dose-dependent negative effect of nitrate on growth. Except for the lowest nitrate concentration (100 mg L− 1 nitrate-N), the histological survey revealed significant changes induced by nitrate in all examined organs
So if I understand correctly, high nitrate levels are more concerning if they came from the oxidation of ammonia from fish waste, because the high initial amount of ammonia and nitrite will be way more dangerous to fish.
Yes, they are the "smoking gun" , but the "bullet" was the ammonia (NH3) and nitrite (NO2) that preceded them.
But, what if the high nitrate concentration was accumulated over a long period of time from relatively low and safe levels of ammonia?
I don't know, <"I've kept fish"> since <"aged water"> was considered a good thing and <"old tank syndrome"> (possibly related to the build up of nitrate) was real issue. I'm still <"not a very good fish keeper">, but water changes and planted tanks have made my life (and the fishes lives) a lot easier.

I honestly don't think that NO3- accumulation is ever going to be an issue for us now, everybody (nearly everybody) changes some water, and, on this forum, we all keep planted tanks and plants are the <"gift that keeps giving">.

cheers Darrel
 
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