I have been researching owning goldfish. I have gone to many people with questions. I have a 30 gallon tank with four small orandas. I was told that is the proper amount for that size tank. I have a fish that stays near the bottom of tank. the rest are on the surface gulping air. I have bought every chemical suggested with no change. I have a water test I use. most are normal. I was told to take out my heater to cool water. it is now at 64 degrees. how do I keep them from low temp. please help