# Adding nitrate to stocked aquarium



## Stevieblue (23 Jul 2014)

Hi all 
I am currently using ei dosing and wandered wether to leave out the nitrate from my mixture as I have quite a heavily stocked aquarium. Recently my nitrate readings have risen which I suppose would do if adding nitrate. Currently nitrates are at 80ppm. Any advice greatly appreciated.


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## EnderUK (23 Jul 2014)

Welcome

I would hate to know what test kits said about my tank. Why don't you just do 75% w/c rather than 50% and still dose the KNO3?

You could also try cut back a little on the KNO3 wait a few weeks and see how your plants are doing, if they're okay cut back a little more. Do this until you notice the plants suffering then up the dosage to the previous period.


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## Dominic (23 Jul 2014)

Hello mate, just wanted to add that i do not trust nitrate test kits much, I usually rely more on observing the health of both fish and plants. Just my opinion! Hope everything pans out


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## Andy D (23 Jul 2014)

As Dominic and other experts on here advise, nitrate tests kits are horribly inaccurate so you may do more harm then good by following what it tells you. Just dose as per the EI instructions and monitor, monitor, monitor.

It is very unlikely the nitrate will get to a level that causes problems.


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## GHNelson (23 Jul 2014)

Hi
I wouldn't bother worrying about it...I have 40/50ppm in my municipal tap water but i still dose KNO3.
Hobby test kits are not that accurate......as stated in previous posts.
hoggie


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## Edvet (23 Jul 2014)

Test kits lie!! (but i guess you gathered that already)


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## sciencefiction (23 Jul 2014)

Here is my visual explanation.
No nitrate added growth as seen in the bottom of the plant,  or rather low nitrate derived in a natural way, and then plenty of nitrate(dry salts) added half way through the ludwiga growth which changed the size of the leaves and density of nodules.
I didn't mind either type of growth or look. All you need to strive for is never have nitrate at zero as that's when problems like algae and sorry looking plants happen. But in low tech tanks or tanks that don't get much cleaning and water changing, I don't add too much nitrate at a time,  I won't go in detail why because I'll be crucified here. As far as your fish go, they don't care about how much you add. There's no decent scientific study that proves nitrates on their own have any affect on fish whatsoever, even at higher levels than you can even would dose in a high tech. The problem is if the nitrate level in your tank is a result of high ammonia to nitrite to nitrate conversion. It's a very exhausting process that changes the chemistry of the tank in a bad way.


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## Stevieblue (23 Jul 2014)

Hi 
Thanks for replys. Iam happy with everything going on in the tank ,seems to be nicely balanced at the mo. Only reason for the question was I had a sudden unexplainable death hence the chemistry set came out. Once I seen the nitrate level (according to test kit )I was thinking of maybe cutting the nitrate out from my mix. But visually looking at the tank I have no concerns other than my lost discus. Suppose these things happen now and then.


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## sciencefiction (23 Jul 2014)

Welcome to the forum Stevie. And sorry for your fish.
 It's most likely a coincidence. However in a heavily stocked, older tank with anaerobic aereas which can be common in planted tanks, you can get nitrAte to nitrIte conversion which is not common but can happen. So  sometimes the problem is not because one adds nitrates but because high nitrates can lead to nitrate to nitrite conversion on regular basis. However, the most probable cause of demise and problem of fish is the amount of ammonia a tank has to deal with and the associated organic build up if plants, cleaning and water changes aren't enough to deal with it.
With all that said, your discus may have died from about thousand other causes.


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## Dominic (24 Jul 2014)

sciencefiction said:


> Here is my visual explanation.
> No nitrate added growth as seen in the bottom of the plant,  or rather low nitrate derived in a natural way, and then plenty of nitrate(dry salts) added half way through the ludwiga growth which changed the size of the leaves and density of nodules.
> I didn't mind either type of growth or look. All you need to strive for is never have nitrate at zero as that's when problems like algae and sorry looking plants happen. But in low tech tanks or tanks that don't get much cleaning and water changing, I don't add too much nitrate at a time,  I won't go in detail why because I'll be crucified here. As far as your fish go, they don't care about how much you add. There's no decent scientific study that proves nitrates on their own have any affect on fish whatsoever, even at higher levels than you can even would dose in a high tech. The problem is if the nitrate level in your tank is a result of high ammonia to nitrite to nitrate conversion. It's a very exhausting process that changes the chemistry of the tank in a bad way.



Does this mean, in terms of fish more sensitive to nitrate, i.e marine fish and corals etc (sorry, unrelated topic) are they more sensitive to the conversion of ammonia to nitrite to nitrate?


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## nickmcmechan (24 Jul 2014)

Dominic said:


> Does this mean, in terms of fish more sensitive to nitrate, i.e marine fish and corals etc (sorry, unrelated topic) are they more sensitive to the conversion of ammonia to nitrite to nitrate?



Can't answer on behalf of science fiction, but I think point is the nitrites, not the sensitivity to nitrates. Nitrites are toxic even in very small amounts, nitrates are not. It's not about the conversion, it's about the presence of nitrites at all.

Nitrate sensitivity causes much debate and most here will heavily dose nitrates in tanks containing species thought to be sensitive to them with no ill effect


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## EnderUK (24 Jul 2014)

Depending on how your tank is setup you could get some surface plants or very fast growing stem plants to mop up all the ammonia, nitrite, nitrate, Plant heavy. Make sure you get your flow and CO2 right,  (ie probably add more in a safe way. I assume you're adding CO2 since you're talking about EI), lights is also important but not so much if you get the flow and co2 sorted. Do big water changes, if you're not happy at doing one big 75% change why don't you do 25% every other day. If you have a healthy heavy planted tank then you really don't need to worry about ammonia.


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## sciencefiction (24 Jul 2014)

Dominic said:


> Does this mean, in terms of fish more sensitive to nitrate, i.e marine fish and corals etc (sorry, unrelated topic) are they more sensitive to the conversion of ammonia to nitrite to nitrate?



I can't argue about saltwater much because the processes and toxicity of things are different, e.g nitrite is less toxic in marine enviorment, there are other chemical reactions in place not so common in freshwater..,etc..
But high organic nitrates indicates previously high presence of ammonia which is toxic to all type of fish. Plus the associated processes and byproducts of them and their effect on fish and water chemistry has to be taken into consideration. The nitrogen cycle involves a lot of oxygen consumption. In high organic environment where lots of organics are present for various reasons, they decompose via oxygen. Ammonia get converted to nitrite and nitrate via oxygen, fish, plants need oxygen, other aerobic bacteria and microorganisms rely on oxygen to support the system, etc.. So high organics lead to high ammonia, low oxygen conditions, possibly nitrate to nitrite conversion in anaerobic areas, nitric acid, etc.. These are enough to stunt your fish or kill them and then one blames it on high nitrates which is just a product/indicator of all that's happened up to then.


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## NatureBoy (24 Jul 2014)

sciencefiction said:


> you can get nitrAte to nitrIte conversion which is not common but can happen


Hi, I'm pretty sure that higher concentrations of nitrate (beyond what is required for healthy plant growth) can result in some being utilised by bacteria in processes that lead to nitrites at levels significant enough to effect fish physiology.

I'm happy with the idea that nitrates alone are not toxic, but whenever I've pushed up the nitrates for a period of over two weeks some fish get sluggish, swim listlessly, lose appetite and seem to have difficulty respiring (flared out gills), however they don't gasp at the surface. Pearling plants suggest water is fully saturated in oxygen, and CO2 levels are safe. A partial water change and the effects are immediately reversed with fish regaining vitality and appetite and displaying normal behaviour. All seems to indicate a gradual increase in the concentration of nitrites. I add nitrates daily but in very small amounts, and have nitrates in tapwater too, I just don't whack in loads without worry about excess for the above reasons.

it supports the idea of mandatory weekly waterchanges in conjunction with EI dosing. Shoot me down.


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## ian_m (24 Jul 2014)

Due to a faulty dosing pump timer I dumped 1litre of EI macro mix into 180l tank giving over 300ppm nitrate for couple of days before I noticed.

Were fish bothered, nope, normal shoaling and food hunting activity. Absolutely no change in their behaviour.

It was only the whirring of the dosing pump that gave the game away.


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## ceg4048 (24 Jul 2014)

NatureBoy said:


> Hi, I'm pretty sure that higher concentrations of nitrate (beyond what is required for healthy plant growth) can result in some being utilised by bacteria in processes that lead to nitrites at levels significant enough to effect fish physiology.


This is not true at all. You have some other problem going on in your tank and it's very easy to blame the boogie man. If I had to guess I'd say it was either a CO2 overdose or low oxygen due to organic pollution.

Pearling plants don't tell you ANYTHING about the saturation of Oxygen within the water. That's another illusion. One illusion built on another.

There is such a thing as nitrate toxicity, but it doesn't happen due to bacteria reducing the NO3 to NO2. It happens inside the fish who produce an enzyme called Nitrate Reductase. Nitrate actually isn't poisonous, it only can become toxic due to the animals body reducing it to Nitrite. However, the concentration levels required for that to happen in tropicals are astronomical.

I mean really people, you change your water and the fish become better - and you blame it on Nitrate? 
There is no "getting better" from NO2 or NH3 poisoning. The damage is permanent, so that should tell you immediately that you have some other problem.

Cheers,


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## NatureBoy (24 Jul 2014)

no one's blaming nitrate or banging on about nitrate toxicity.

going easy on dosing and I've not seen the behaviour that is described in this article. 

http://freshaquarium.about.com/cs/disease/p/nitritepoison.htm


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## ceg4048 (24 Jul 2014)

Well going easy on dosing has other secondary effects, such as less organic pollution, which causes less oxygen depletion.

The article also clearly indicates that the NO2 concentration rise follows on the heels of NH3 concentration rise, whereas you clearly blamed Nitrate. Was this a typo?



NatureBoy said:


> Hi, I'm pretty sure that higher concentrations of nitrate (beyond what is required for healthy plant growth) can result in some being utilised by bacteria in processes that lead to nitrites at levels significant enough to effect fish physiology


That sounds like banging on about nitrate toxicity.

Is it meant to imply that only Nitrite toxicity causes listlessness and rapid gill movement?

When dosing heavily without performing a large water change one will always risk pollution because plants will produce massive amounts of organic waste including proteins, lipids and carbohydrates. So if you did experience the lower rate of toxicity syndrome from lower rates of nitrite then it would be more rational to conclude that your tank has produced less organic pollution and that there is less NH3 production from that lowered level of pollution, which also results in less oxidation of the NH3 to NO2.

That's why eutrophic dosing requires larger and more frequent water changes. It's NOT to lower the NO3 but instead to lower the pollution that results from the plants elevated metabolism.

Cheers,


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## Alje (24 Jul 2014)

As the saying goes, 'the solution to pollution is dilution'
If in doubt good quality water change


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## NatureBoy (24 Jul 2014)

...





NatureBoy said:


> higher concentrations of nitrate (beyond what is required for healthy plant growth) can result in some being utilised by bacteria in processes that lead to nitrites at levels significant enough to effect fish physiology.



I'm merely suggesting that the three ways that nitrates can be _converted_ by bacteria to nitrites could _result in_ an accumulation of nitrites in some aquariums. Diana Walstad references research that suggests that bacterial utilisation of nitrates leading to end point of nitrite could be quite common (without further conversion to N2)


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## ceg4048 (24 Jul 2014)

So why would the nitrite converted by bacteria not then be immediately converted back to Nitrate by the nitrifying bacteria in your filter and sediment? Isn't that the job of  the nitrite oxidizing bacteria Nitrospira, Nitrobacter, Nitrococcus, and Nitrospina? Wouldn't their populations increase simply by virtue of the extra availability of NO2? 

The fact that many of us dose whack in loads of nitrates on a regular basis without having any of these issues suggest that NO2 accumulation is not common at all.

To test your theory you should perform massive water changes while increasing the nitrate levels even after the water changes. I did this repeatedly and calculated what the nitrate buildup levels should be assuming some nominal uptake rate. I then added those NO3 values after the water change to return the NO3 levels to the calculated buildup levels and saw zero negative effects. Some fish bred under those conditions.

So in that way we can separate the effects of NO3 buildup from the effects of organic pollution. If NO2 accumulation were a problem from NO3 conversion then the fish would have suffered debilitating effects in the days following the water change.

Similar to that reported by ian_m, London Dragon dosed 10X EI inadvertently in his shrimp tank for weeks until he realized his miscalculation. He saw no negative effects. So there is too much evidence to the contrary. Dosing small amounts causes less pollution so that easily explains why you can get away with not changing your water frequently. In fact we suggest that if you want to dose EI without the manic water changes then just dose less.

Cheers,


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## sciencefiction (24 Jul 2014)

You would need the proper conditions to get nitrate to nitrite conversion.
In the examples given here where people have no problem, tanks are all high techs with fast growing plants moping nitrogen of any kind even such as ammonia and nitrites regardless of their origin, large water changes weekly further diluting any possible toxin that may arise, etc...So you'll hardly have any issues with toxic nitrogen. But the point is it's not impossible to get nitrate to nitrite conversion and actually suffer consequences in certain setups where in that exact moment your plants may not be very efficient or your nitrifying bacteria is used to a certain levels of nitrites and can't handle a sudden extra load. And water changes are not that big or that often to counteract the issue.


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## EnderUK (25 Jul 2014)

I'm no chemist, I have no idea what is going on in my tank. I just do big water changes and this means I really don't need to know all this chemistry you guys keep going on about. It kind of seems you're arguing the same points to me just from different approaches. Solution is the water change.


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## ceg4048 (25 Jul 2014)

It's actually a very important argument and no, we are not arguing the same points at all. On the one hand, there is an opinion, the essence of which is that adding inorganic nitrate to the tank causes that NO3 to be converted to toxic NO2 directly. The counter argument is that the toxicity in a tank is not due to direct conversion, but instead, is a result of plants and fish living in their own toilet and that the more they are fed, the more the toilet is filled.

This is a huge difference because those who believe that nitrate is a boogie man will fear  to add KNO3 to the tank, and this fear sometimes drives them to extreme action such as spending money for ~special filter media" to eradicate nitrate. By attempting to eliminate nitrate in a planted tank hobbyist can do things that are actually counterproductive to the tank system. Also, when there are problems in the tank, how you troubleshoot and what the procedure you use are determined by which argument you believe.

Those who do not fear nitrate salts understand that living in a toilet is a problem and that the problem can be mitigated by frequent flushing. You can still eat well and be healthy as long as you frequently flush your toilet. If you eat well and don't flush your toilets you will suffer problems, but the problems are not because you are eating well, it will be because the toilet becomes filthy. That's more than a different approach.

So understanding the nature of, and mechanism of the toxicity is very important because what you do to your tank is based on what you believe, and what you do directly affects your success rate. We know from experience that many people fear to perform large and frequent water changes under the misguided mantra that they must "keep their parameters the same". We are attempting to eradicate that misguidance by explaining a bit more about those parameters.

So my objective is to eliminate the fear of nitrate because I see it as an obstacle to success. Using some obscure set of environmental conditions as a basis for avoiding the second most important nutrient misses the point entirely. Not changing your water and then assuming is was because of Nitrate conversion to Nitrite is one of those assumptions that causes more problems than it solves.

Cheers,


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## NatureBoy (25 Jul 2014)

sciencefiction said:


> You would need the proper conditions to get nitrate to nitrite conversion.
> In the examples given here where people have no problem, tanks are all high techs with fast growing plants moping nitrogen of any kind even such as ammonia and nitrites regardless of their origin, large water changes weekly further diluting any possible toxin that may arise, etc...So you'll hardly have any issues with toxic nitrogen. But the point is it's not impossible to get nitrate to nitrite conversion and actually suffer consequences in certain setups where in that exact moment your plants may not be very efficient or your nitrifying bacteria is used to a certain levels of nitrites and can't handle a sudden extra load. And water changes are not that big or that often to counteract the issue.



exactly my point...even if you have maximum growth and uptake, bacteria are also always going to take advantage of any additional nitrate that's floating around. One way is the process that leads to denitrification and eventual loss of nitrogen as N2, another is down a different path like nitrate respiration, etc. The greater the concentration of nitrate, the greater the bump in the interim stage of nitrite, before conversion to N2, etc, . You could dump 300ppm nitrate happily and then do a big water change a couple of days later and all will be fine, but leave that 300ppm of nitrate for a couple of weeks and you'll get a bump in nitrites as bacterial populations that feed on nitrate begin to chow down. 

This is not knocking EI: it simply advocates the fundamental of doing a water change before nitrite levels become an issue.[DOUBLEPOST=1406277264][/DOUBLEPOST]





ceg4048 said:


> So my objective is to eliminate the fear of nitrate because I see it as an obstacle to success. Using some obscure set of environmental conditions as a basis for avoiding the second most important nutrient misses the point entirely. Not changing your water and then assuming is was because of Nitrate conversion to Nitrite is one of those assumptions that causes more problems than it solves.



I know you are passionate about the benefits of giving plants food to eat, as am I. That is why I give my plants a daily feed of nitrates et al, I am not afraid of this and will never eliminate or seek to eliminate a source of nitrogen in the water column. Scouts honour.



ceg4048 said:


> On the one hand, there is an opinion, the essence of which is that adding inorganic nitrate to the tank causes that NO3 to be converted to toxic NO2 directly. The counter argument is that the toxicity in a tank is not due to direct conversion, but instead, is a result of plants and fish living in their own toilet and that the more they are fed, the more the toilet is filled


It is definitely not an opinion but scientific fact that nitrates get converted to nitrites, a toxin we should seek to dilute out of the water column. It is more of an opinion to assume that metabolites of plant growth create an imminent toxic threat to fish and plants that needs to be rectified by large water changes. Either way we are suggesting a water change in conjunction with EI.


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## ceg4048 (25 Jul 2014)

The basic EI procedure has always advocated large weekly water changes. That's nothing new. The opinion that I'm talking about is that you believe nitrite conversion is a more imminent threat than hypoxia due to nitrification. The nitrite oxidizing bacteria are very aggressive so it is not likely that there would be a buildup of nitrite. The rate at which they oxidize nitrite will be higher than the rate at which nitrate will be reduced to nitrite, so it's really not something to worry about. You also assumed that your fish were suffering from nitrite poisoning without any scientific evidence just because the symptoms appeared to be similar to that describe in the nitrite toxicity article. 

As I mentioned, hypoxia due to nitrification is always a more imminent threat than nitrite due to denitrification and as I mentioned, the damage due to nitrite poisoning is permanent. Your fish would not have recovered immediately after a water change, especially if it was a recurring situation. Nitrite and ammonia irreparably damage the gills so there would not have been an immediate recovery. CO2 poisoning and hypoxia can be recovered from much more easily so those are much more likely possibilities.

Cheers,


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## NatureBoy (25 Jul 2014)

I'm putting forward a set of plausible statements that may have led to the behaviour I observed in my fish, nothing more nothing less. It is an opinion, as are basically most of the statements you make in the above post such as 



ceg4048 said:


> The rate at which they oxidize nitrite will be higher than the rate at which nitrate will be reduced to nitrite





ceg4048 said:


> The nitrite oxidizing bacteria are very aggressive so it is not likely that there would be a buildup of nitrit





ceg4048 said:


> hypoxia due to nitrification is always a more imminent threat than nitrite due to denitrification





ceg4048 said:


> the damage due to nitrite poisoning is permanent





ceg4048 said:


> Nitrite and ammonia irreparably damage the gills so there would not have been an immediate recovery





ceg4048 said:


> CO2 poisoning and hypoxia can be recovered from much more easily



How many of these claims are backed by scientific fact that you can reference?


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## dw1305 (25 Jul 2014)

Hi all,
I think the real problem with this question is that there isn't much scientific data that *just looks at NO3*, it nearly all looks at nitrate levels as the "smoking gun" of the microbial oxidation of NH3 and NO2. This is understandable because, with the exception of addition by aquascapers, NO3 is usually a marker of organic pollution.

The best paper I could find (and that is freely available) is "<A Review of Nitrate Toxicity to Freshwater Aquatic Organisms>", which looks at both acute toxicity and long term effects.

Personally I like to keep the levels of all nutrients (including NO3) fairly low. My primary aim is to use plants as a method for maintaining very high quality water, so I'm only ever adding any nutrients if levels (of the limiting nutrient) drop so low active plant growth ceases.

This was the idea behind the "<Duckweed Index>" (not my idea originally, I adapted it from  <The Charms of Duckweed - Practical Duckweed: Application Areas>), and came directly from the concept of reduction of Biochemical Oxygen Demand (BOD) <http://www.planetcatfish.com/forum/viewtopic.php?f=4&t=35930> from our work on the re-mediation of landfill leachate, which you could just regard as uber polluted tank water.

cheers Darrel


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## NatureBoy (25 Jul 2014)

dw1305 said:


> Hi all,
> I think the real problem with this question is that there isn't much scientific data that *just looks at NO3*, it nearly all looks at nitrate levels as the "smoking gun" of the microbial oxidation of NH3 and NO2. This is understandable because, with the exception of addition by aquascapers, NO3 is usually a marker of organic pollution.
> 
> The best paper I could find (and that is freely available) is "<A Review of Nitrate Toxicity to Freshwater Aquatic Organisms>", which looks at both acute toxicity and long term effects.
> ...


Hi Darrel

What are your thoughts on nitrates in water column being converted to nitrites in a concentration that could be detrimental to fauna either through transition through denitrification, incomplete denitrification, incomplete DAP or bacterial respiration of nitrate?

My thinking being: the greater the concentration of nitrate the greater the potential for a equilibrium amount of nitrite that could be detrimental...


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## Spnl (26 Jul 2014)

Nature boy said:
My thinking being: the greater the concentration of nitrate the greater the potential for a equilibrium amount of nitrite that could be detrimental...

I think this is a false assumption. Denitrification is an anaerobic process, the main driver for conversion of NO3 to NO2 is low oxygen, not high nitrate.
Given the conditions we aim for in an EI dosed tank, surely there should be little in the way of anaerobic conditions. Possibly only in deep substrate or a badly clogged up filter.


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## NatureBoy (26 Jul 2014)

Spnl said:


> Nature boy said:
> My thinking being: the greater the concentration of nitrate the greater the potential for a equilibrium amount of nitrite that could be detrimental...
> 
> I think this is a false assumption. Denitrification is an anaerobic process, the main driver for conversion of NO3 to NO2 is low oxygen, not high nitrate.
> Given the conditions we aim for in an EI dosed tank, surely there should be little in the way of anaerobic conditions. Possibly only in deep substrate or a badly clogged up filter.


nitrifying / denitrifiying bacteria co exist in symbiotic biofilms, as the nitrifying bacteria use up the available oxygen, the anaerobic conditions exist for nitrate to be the next available electron acceptor. This happens all over the aquarium where bacteria can form biofilms.

Diana Walstad's book Ecology of Planted Aquarium has an amazing chapter on the role of bacteria in the aquarium. An interesting experiment she references traced the fate of nitrogen over 27 days through additions of nitrates and ammonia to planted tanks. What is amazing is the amount of nitrogen lost as nitrogen gas, as much as 80% in one case - this indicates that denitrification (use of nitrate as food for bacteria) is a major player in a healthy balanced aquarium.

She went on to perform her own experiments on soil substrates alone: "I found that even in bottles containing a hefty 250 mg/l nitrates, nitrates started declining substantially within one week and were completely gone within 1 month. During this experiment, *nitrites appeared in the water at 3 days* indicating that some nitrate respiration was also occuring...."


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## dw1305 (26 Jul 2014)

Hi all, 





NatureBoy said:


> nitrifying / denitrifiying bacteria co exist in symbiotic biofilms, as the nitrifying bacteria use up the available oxygen, the anaerobic conditions exist for nitrate to be the next available electron acceptor.


 They can do, this is what used to happen with the trickle filters with the landfill leachate, but I think "Spnl" is probably right, as long as everything is aerobic the only possibility for denitrification is in the anaerobic zone of the substrate. 

I've got the greatest respect for Diana Walstad, and if I only owned one fish keeping book it would be "_Ecology ....._", but her initial method didn't have water circulation, or water changes, and these factors make a lot of difference. 

In the planted tank with EI, a lot of flow and added CO2 my suspicion would be that the vast majority of NO3 is taken up by the plants. Personally CO2 addition or EI aren't routes I'm ever likely to go down, and because I only keep heavily planted tanks (with plants with the access to aerial CO2), I'd be quite surprised if I ever have more than about 10 ppm NO3. 

cheers Darrel


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## NatureBoy (26 Jul 2014)

in conclusion then: add nitrate if you feel / see the need to but keep up with the water changes


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## sciencefiction (26 Jul 2014)

It depends on the bacteria flourishing in particular setups. Most of nitrate dissimilation occurs in low oxygen conditions but as Darrel pointed out it's been studied to happen in trickle filters as well. Some bacteria dissimilate nitrate to ammonia and nitrite, others to elemental N2 but nitrite accumulation can occur. These types probably prefer low oxygen conditions but full denitrification without nitrite accumulation depends on many factors, like Ph and even light intensities, available carbon, type of carbon, and they can be facultative anaerobs, meaning if there's no ammonia, they'd reduce nitrates instead. Some are autotrophs, some heterotrophs.
But there are types nitrate assimilating bacteria which would reduce nitrates in aerobic as well as anaerobic conditions so it can happen in "clean" tanks.  One doesn't know what they have in their tank really and can't be sure of the processes going on.
For the most part we are just talking theoretical stuff here and not really suffering or needing to worry about any of that.


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## dw1305 (28 Jul 2014)

Hi all, 





sciencefiction said:


> as Darrel pointed out it's been studied to happen in trickle filters as well


 It is one of the big areas of research in trickle filters, the aim is to have a filter bed material that sustains a biofilm, but one that isn't so thick that it impedes the flow of air and "water". 

What you really want is a material that is self cleaning to some degree, so when you get the situation in the schematic (from <http://en.wikipedia.org/wiki/Trickling_filter>) the biofilm layer sloughs off. 




 
What has tended to happen with newer systems in Europe and N. America is that people have gone for either totally anaerobic (has advantages of reducing smell, using less land area and producing methane), or more fully aerobic systems with "aerated biofilters", which are basically trickle filters in a tower using forced aeration from the bottom of the tower. 

In the tropics a lot of work has been on lagoon systems with floating plants. People have also tried simultaneous nitrification ~ denitrification on a commercial scale in the ORBAL process <http://www.wateronline.com/doc/orbal-multichannel-oxidation-system-0001>, but there are quite a lot of "moving parts" where things can go wrong.





sciencefiction said:


> But there are types nitrate assimilating bacteria which would reduce nitrates in aerobic as well as anaerobic conditions so it can happen in "clean" tanks.


 I think you can really ignore reduction reactions outside of the substrate. 

Fundamentally as long as you keep the filter material and tank water well oxygenated you get NH3(NH4+) > NO2 > NO3 > removal by plants. You also need a CO2/HCO3-  source, but water circulation will help with this even during active photosynthesis. 

2 NH4+ + 3 O2 → 2 NO2- + 2 H2O + 4 H+ 

2 NO2- + 1 O2 → 2 NO3- 

NH3 + O2 → NO2− + 3H+ + 2e−
NO2− + H2O → NO3− + 2H+ + 2e−
Oxygen is really the key, which is why the BOD concept is so useful.

cheers Darrel


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