All of my fish are swimming at the top of the tank

Question
I have had my aquarium for about 3-4 months, day before yesterday I bought a couple of new fish.  Yesterday they all started swimming at the top, almost like they are not getting enough air!   Are they sick?  I know there is enough oxygen, the pump is working very well!

Your opinion would be most helpful!

Answer
Hello,

My first guess would be that there is too many nitrites in the water level. Nitrites are highly toxic to fish. You should test your water right away. If the levels are high (0.3 ppm or above) then you should immediately change 25% of the water and add a denitrifier (such as Cycle). Reduce the amount of food you are feeding your fish (to eliminate excess waste).

If you discover that it is not nitrite then it could be a bacterial gill disease. You should treat your tank with an antibacterial- such as Melafix.

I hope this helps.

Good-luck,
From Stephanie