I dont think water changes have anything thing to do with the cycle other than reducing nitrates. the bacteria involved in the cycle are mainly in the gravel and filters. if you cleaned your filters you may have a nitrite spike if you removed too much of the good bacteria. I am no expert but this is my understanding.Xenon said:Could the fact that you have done two quick water changes cause this spike as the nitrites need to build back up? Maybe you stressed the tank a little with doing two back to back changes? Just a thought....If you think the levels are getting to high, quarantine the fish until it seems better....I wouldnt take a chance.