On Tuesday I did water changes on 5 of the 6 tanks we have like usual. Last night when we got home we noticed all of our cichlids at the top of the tank gasping for air. I tested the water and the nitrites were at about 3. We had 4 dead fish. I did an immediate 80% water change. this morning same thing. 3 more dead. Nitrites about 2. another massive water change. Obviously something I did threw the tank into a minI cycle of some kind and of course I had to go to work and could not deal with it until after work. Got home and lost one more fish, Nitrites were at about .5. I ran to the fish store got some seeded bio rings and some prime. Added the bio rings to the cannister filter added the prime dopped the water level below the spray bar to help airate the water and they seem to be doing ok....I am so bummed. I lost my Prize electric yellow and a couple of my favorite catfish along with several others. I just can't imagine I forgot to condition the water I changed, but maybe I did. Something happened to start the cycle and it was something I did. ......................I bet I'll never let that happen again.