"We have a 75 gallon fresh water aquarium with 7 fish. The fancy goldfish have taken to laying on the bottom of the tank except when the light comes on. The water temp is fine and the fish seem to be okay once the light goes on. What could be causing this? We have had our fish for quite awhile and we don't want to lose them. Please let me know what may be causing this and what I can do to rectify this problem."