Innactive goldfish.

Question
QUESTION: I have two goldfish in a five gallon tank. Its getting colder now. Winters coming. They were fine until last week when they gradually slowed in activeness. The tank is clean and i cleaned it two days before. Now they normally spend their time on the top region of the tank and seem to always take air from the surface with their mouths. Their dosal fin is slightly closed unless they are startled. On the bottom back part of the dosal fin is slightly opaque. Nothing on any other fins. Except for that there is no other symptoms distinguishable(no parasites, no discoloration, no shineless ness) It could be fin rot but the tank is very clean. Its sort of a vail tail- maybe the dropping temperature is affecting it. They were originally in an outside pond so i don't know why cold would affect them(temperature doesn't drop below 12'C)
Tell me whats wrong with them.
Thanks.

ANSWER: Km,          Two things that tank is waaaaaaaaaaaaay too small. The reason they are hanging at the top may be heat (65 to 72). It could also be lack of oxygen which is what I think it is. The way they drink is by osmosis...fancy word for absorbing water and relieving themselves of liquid wastes which also takes the O2 out of the water. First I would get a larger tank. Make sure you have the proper filtration and for goldies add an airstone to agitate the top of the water and envelope more oxygen into it. They give off tons of wastes....this causes ammonia to build up in the water and can cause their fins to rot. Again because your tank is small it builds up fast and you don't want to have to change the water every 2 days it is too stressful. Good Luck, Tina

---------- FOLLOW-UP ----------

QUESTION: Thanks for answering. I do have an undergravel filter which is run by an air pump. So the water surface is agitated. Now the fin roots are a bit red and fin edges are damaged. It definitely should be fin rot. Does the temperature affect wailtails (I've read it somewhere). I'll be buying medicine tomorrow. Any comments?

Answer
Km,          Your under gravel is a biological filtration...you still need an active mechanical filtration with carbon to remove ammonias and other kiquid wastes from the water. Medication is not going to fix your problem unfortunately. An undergravel without powerheads is pretty much useless. There is not enough force to actually bring the water thropugh the undergravel. You might want to add a small power head on one side and cap the other off. Again too much fish not enough water....Good Luck , Tina