I have a 75g tank of African cichlids and there are dying 1 per week. The first one had white cotton like substance on his body. I treated the tank with Maracyn for 3 days I thought everything was good then another fish got sick. I removed him from the tank and setup a 10g hospital tank and treating both with Maracyn it’s been 6 days. The fish in the 10g still lives but not eating. After 3 days I stop treatment (75g ), this morning I found one dead and one sick with no cotton like substance but with a lost in color. I moved the sick one to the hospital tank. My question is what wrong with them and why are they getting sick? My water level are good and temp is 78-80 degrees.