Nitrate Being Converted Into Nitrite?

[mark4785]

My aquarium currently contains 4 albino corydoras which are all continually gasping for air. I have tested my ammonia and nitrite levels and the former is at 0 ppm while the latter is between 0 and 0.25 ppm.
 
I'm finding that every time I dose the aquarium with nitrate (a fertiliser for the plants), the drop-checkers are turning yellow (indicating very high co2) and the nitrite level is going up to 0 - 0.25 ppm.
 
I have come across an article on the internet ( http/www.pondcrisis.com/a_nitrite.html ) which indicates that under hypoxic conditions (low oxygen) nitrate can be converted back into nitrite by a certain strand of bacteria. Is this what is happening in my aquarium? If it is, why would the tank become hypoxic only after introducing the nitrate fertiliser?
 
I have been using the said nitrate fertiliser for about 5 years and used it today on a separate tank; the fish in there are not hypoxic and have been solidly healthy for a good 2 years.
 
I'm really confused at this point!

 

[dave840f1]

Its seems to me the plants are not using all the fert's you are adding to the tank. It is possible they are reducing the amount of Oxygen in the water. Have you tested for this. I would do a 40/50% water change now and stop putting fert's in.

 

[KirkyArcher]

 the drop-checkers are turning yellow (indicating very high co2)

 also Indicating acidic water I'd guess it'll read about a PH of 6.2 - 6.6

 

[mark4785]

Its seems to me the plants are not using all the fert's you are adding to the tank. It is possible they are reducing the amount of Oxygen in the water. Have you tested for this. I would do a 40/50% water change now and stop putting fert's in.

 
The plants seem to be growing fine. I know plants can sometimes grow slightly when in darkness by using up oxygen but for the most part i'm sure they are utilising the injected co2 and some of the nutrients as they would not grow at such a fast rate if they were using oxygen. As I always dose an excess of nutrients (nitrate and phosphate) it is definitely the case that they won't be using all of it up; this doesn't ever cause any problems in any of my other set-ups.
 
Unfortunately, I may have found out why the nitrite is appearing shortly after dosing nitrate. The article I linked to states that under hypoxic conditions, nitrate can be converted into nitrite, presumably by an undesirable blend of filter bacteria that grows in low oxygen environments. This would be feasible as my co2 diffuser is situated below all of the filter media and is wrapped in cotton wool to help the co2 bubbles fully dissolved into the water. Presumably the water that is going through the filter media is totally devoid of oxygen, thus creating a state of total hypoxia in the filter system.
 
Given the above, I've removed the co2 diffuser from the internal filter system and put it on the outside of the internal filter so as to allow oxygen, rather than carbonic acid, to travel through the filter system. This O2 should hopefully induce nitrosomonas and nitrobacter colonies (the latter of which I need to cultivate which will convert nitrite into nitrate rather than nitrate into nitrite!) to grow. I have 'seeded' the filtration system with a pond filter sponge in the hope that the beneficial bacteria on it will replicate onto the formerly redundant, carbonic acid soaked, filtration media.
 
Edit:
 
I just like to ask if anyone knows of the name of the blend of bacteria that is responsible for converting nitrate to nitrite? It would be excellent to know more about it so that I can ensure it doesn't colonise in my filter system ever again!
 
Thanks.

 

[dave840f1]

Sorry I don't have the names of the bacteria etc. But It is my understanding that when the Nitrate produces Nitrogen  this Nitrogen reacts with whatever Ammonium you have in your tank (fish waist being continuous) which turns into Nitrite, hence you could experience a spike in the Nitrite. This is only my theory so I may be wrong.

 

[TwoTankAmin]

None of what you have stated is correct. For nitrate to be converted to nitrite requires an almost complete absence of oxygen. There is no way there is this low an amount of O in your tank water, if there were, all your fish are floating. The conditions needed for this might be present in deep enough substrate.
 

 
Presumably the water that is going through the filter media is totally devoid of oxygen, thus creating a state of total hypoxia in the filter system.

 
Not possible since the ammonia and nitrite oxidizing  bacteria both need oxygen to work. So do the other heterotrophic bacteria in our tanks.
 
My bet is you are getting a false reading or else misreading the results. On an API test kit a nitrite reading of .25 ppm or below for a short time is really not a concern anyhow.

 

[dave840f1]

This is only what I looked up on the internet, I will try and find the link again and try and post it. I know Nitrate needs a oxygen free environment to produce Hydrogen
 
I found the link but I don't know how to transfer it to this post.
 
I just realise who you are sorry. Are you getting back on your feet, hope you are on the mend.

 

[mark4785]

None of what you have stated is correct. For nitrate to be converted to nitrite requires an almost complete absence of oxygen. There is no way there is this low an amount of O in your tank water, if there were, all your fish are floating. The conditions needed for this might be present in deep enough substrate.
 

 
Presumably the water that is going through the filter media is totally devoid of oxygen, thus creating a state of total hypoxia in the filter system.

 
Not possible since the ammonia and nitrite oxidizing  bacteria both need oxygen to work. So do the other heterotrophic bacteria in our tanks.
 
My bet is you are getting a false reading or else misreading the results. On an API test kit a nitrite reading of .25 ppm or below for a short time is really not a concern anyhow.

 
Some fish were floating and nearly dead until I removed them.
 
How could the ammonia be oxidising into nitrite when there is no traceable ammonia with a total-ammonia test kit and ammonia test kit to begin with? I'm using the API liquid test kit which has always found problems with water quality alongside troubling fish symptoms so I don't think the test kit is to blame here.
 
I've now removed the co2 diffuser from the bottom of the filtration system and placed it underneath a powerhead on the outside of the filtration system. Since doing this I'm finding that when I dose inorganic nitrate, it is no longer being converted to nitrite; this was previously occurring within a matter of minutes. I think it would be reasonable to presume that a small confined space in a filter was hypoxic and high in inorganic and organic nitrate and therefore allowing nitrite to be cultivated from nitrate.