Nitrite is high in freshwater tank

Question
To: Nathan

I have 55 gallon fish tank.  I have discus fish and angel fish in the tank.  I notice my Nitrite is 5.0 and the ph is 6.4.  I have try not to feed the fish for 1 day only and change the water 15 gallon already.  Also I input stability in the tank.  The tmeperature is 84 degree. What else I can do to reduce the Nitrite level.  I have driftwood and live plant in the tank.

Answer
Hi Alice,

How long has this tank been set up? Judging from the fact that you have Discus fish, I'll assume that you are at least a fishkeeper with a good amount of experience. Nitrite can be high because of many reasons - the main cause is that the tank is still cycling (going through the nitrogen cycle). if this tank is older than 4 months, this is very unlikely. However, if you manage to destroy some of the beneficial bacteria living in your filter/tank, this can also cause high nitrites.

Have you done any of the following things recently?

-Changed much of the filter media
-Replaced the substrate
-Added a chemical such as snail killer, anti-bacterial medication, etc?
-Changed more than 50-75% of the water?
-Completely stripped down and cleaned the tank? (worst case scenario!!!!)
Completely cleaned out the filter?

If yes, then there's a good chance that you killed off a large number of beneficial bacteria. Don't worry - in about a week or two, they will re-establish and you will have zero nitrites again. For now, perform a 10% water change daily, until it's under control. Discus will NOT tolerate a high Nitrite level!!! Right now, perform a 30% water change.

If necessary, you can add a nitrite-removing chemical (only if REALLY necessary!)  if the levels keep going up (unlikely). These are available at your local fish store, but remember - water changes are best!

Good luck, and Happy Fishkeeping!