water change= dead cichlids

Question
I have a 100 gallon tank (has been set up over 2 years now). A water change was done yesterday, and today I rinsed parts of the filtration system. I did not do a complete job because I knew it would destroy the needed bacteria. Immediately after hooking filter up, 2 of the baby cichlids died, and I currently have a blue johanni lying on it side. His gills are moving, color is good but he is just lying there. All other fish are swimming fine. What happened? What can I do to help this fish survive?

Answer
I would start with a water test to see what the tank water chemistry is compared to the tap water that you used to fill the tank back up with.  How much water did you take out???? Add some salt to the water... It sounds like the tank is toxic... let me know... dave