Specs for the tank are as follows. 40 gallon breeder, 82*, emperor 400 biowheel filter and a smaller aquaclear(maybe the 50?). Usually I do 1-2x 50% wc a week. I did a 50% change on Saturday then went away until Sunday night. They were not fed while I was away. I did another 50% wc yesterday. This morning my only female geophagus pellegrini was dead and a few of my other fish look like they may be on their way out. I can't see any physical reason for them to be dying although they are flashing on the rocks. I tested the water this morning and the results are Ammonia 0ppm Nitrite 0ppm Nitrate 0ppm. I just turned the heat up a couple degrees but have not yet added salt since I have an eel in the tank. I didn't know how salt would effect him. How much salt is safe to add with the eel? Any ideas what my be wrong with my fish? Help!!!