I don't understand. My tank is fully cycled I thought I had an ammonia problem but it turns out it was the test kit. Everything else is good. Did a large water change today because I thought I had an ammonia spike. The fish seem to be breathing really fast. I had two new discus I got yesterday but I brought them back because I didnt want them to die. But all my Tetras and 2 blue rams are breathing fast. I had to turn the temp up a little for the discus but since there gone I turned it down thinking that was it. I have the airstone going. I've since discontinued the use of c02. What else could it be? When you do water changes how do you dechlorinate the water? fill a bucket with the correct amount of prime/stress coat or what ever. Then poor it in. Is there a step I'm missing maybe they are being hurt by the chlorine?