My daughter has a 55 gal. tank with assorted africans. This is a well established tank, it has been going for about 8 years. They have not added any new fish since January. About 2-3 months ago, they started losing fish. So far, they have lost about 8 fish. One by one, the fish would get sick with whatever they had. It would last about 2 weeks, then it would die. It resembles a bacterial infection and they have treated the tank with all different types of medications and done all of the proper water changes. They have tested the water, and all of the water levels come back with in normal ranges. Whatever it is, it is pretty contagious to the fish. Any suggestions on what they should do? :1zhelp: