I recently got a 5 gallon fish tank and bought six tetra fish. In less than one week 2 of them had bulging eyes and white growths near their mouths. I went to the store and got penicillian drops and treated for 4 days. It didnt look like the fish were eating it. On day 3 1 fish died and on day 4 the other one did. Now another fish is listing to one side while he swims. His eyes are bulging and no white growths. What should I do? What could be causing this? I appreciate any help!!