I don't think my fish died of disease. My water tests right on ! I haven't lost anything from my salt water tank. I have lost 2 gourmais from my goldfish tank. The goldfish are doing well, but I know the tank is overcrowded. I think I lost 2 cats from my parrot fish tank. I'll have to look more closely later. It is a 30 gallon with 3 zebras, 3 catfish ( ? ) & a parrot fish.I don't call that overcrowed, but I guess the parrot fish may. I'm buying no more fish. It will be survival of the fittest & let nature run its course. What do you think ?