How many goldfish have you got in the tank? Goldfish are any water fish. They grow faster and healthier with warm water. The grow slower and not as healthy in cold water. Cold water is easier for people who aren't dedicated fish keepers because they fish need less maintenence. That only works out for the better of the fish because they suffer less from the lack of care when in cold water. I prefer to keep mine at 76-78F. I use little more than motorized sponge filters in my tanks. It provides biological filtration to keep ammonia at 0. It does not provide much mechanical filtration (aka: the dirt at the bottom of the tank). I take care of that myself with the syphon.