I agree with Biff and Reef.
If you dont have room or the funds for an RO unit,you can get RO water at wal-mart for 33 cents a gallon.
If your using flakes and pellets to feed,switch over to frozen foods.
Plus,If your getting a reading on nitrits,then you got a problem some where.
I'll bet you,ve done something to throw your tank into another cycle.