||05-20-2012 08:05 PM
This question is asked every summer.:-) But the answer is the same.
Temperature variations occur in the wild and fish will generally adapt. If the daytime temperature in the room reaches 85F then the aquarium will be that warm too; while the larger the tank the longer it takes to warm, the average home aquarium will eventually heat up to the room.
It is better to leave this, than do something that results in up and down swings. The cold water/ice floating/water changes is not advisable, and these cause rapid temperature fluctuations that are stressful on fish. If it is really hot, opening the cover (but many fish will jump, so use caution), turning off the tank lights (if no live plants, leave the lights off; if plants, turn the lift off earlier in the day), and aiming a small fan across the surface can help. In the tank, increase water circulation (even add an airstone) to keep oxygen entering the water, since the warmer the water the less oxygen it can hold and fish have to work harder to get it. Overnight, the room will likely cool a bit, as will the tank with it.
Don't feed as much, even missing alternate days. It takes energy for fish to eat, and this adds to the sttress in high temperatures. Keep the fish as calm as possible. If they can just "chill out" under a plant leaf they will be better; just as we on hot days like to sit quietly in the shade.
I have all my tanks in a fishroom, and it will get well over 90F in the summer, in the room and the tanks. I now have a portable air conditioner in this room, that keeps it about 82F on hot days. But before I got this, the tanks were left alone and I never lost a fish. It will cool at night, so it is not the same as a constant too-high temperature.