I have an 125 gallon african cichlid tank which has been in use for 2 years. I bought a cobalt blue cichlid with the red dorsal fin 2 days ago to add to my beautiful tank. Well I do not have a hospital tank for new additions so after acclimation I put the fish right in. Yesterday one of my auratus appeared to have costia,so today I treated the tank with rid-ich after a 25% water change. The first few hours the fish were fine. Oddly enough it was when I left to get more rock for the aquarium and returned to find my tank extremely cloudy and half of my fish DEAD .The rest of the fish were gasping for air at the top of the tank. I did a quick 50% water change and the survivors are acting better. What in the world happened, I have used rid-ich before with no problem before. I am devastated . Any idea what happened or what I could do to help survivors? More water changes?