Everything Fishy

Heater testing is done in North Texas, where our temperatures range from lows of -20 to highs of 110, at different times of year. Room temperature in the winter tends to be 70 to 72 degrees. If your aquarium is in a room with much cooler temperatures, your tank may need a higher wattage heater than the recommended size. Warmer room temperatures cause warmer tank temperatures. I unplug my heaters at home in the summer, since the room temp is kept around 80 degrees. I leave my heaters on during the summer in chilly office buildings.

Heater size is important. I prefer to use 2 smaller heaters rather than one large one, especially on large tanks with expensive stock. I'm putting a 300 watt heater on this page, but I personally recommend purchasing two 100 to 150 watt heaters, and putting one at each end of the tank as a failsafe.

The older style 'Hang on Tank' heaters can be very reliable performers, but never place one over an air stone, or in an area where air bubbles will be bursting around it. The best heaters still fail some day. (Average lifespan for submersibles that are totally submersed: about 2 to 3 years for my Acura heaters in use 24 / 7. Visitherm submersibles are in formal testing this year, but I just threw out a 5 year old visitherm with a 'dead' thermostat, always on or always off. Since it was used sporadically, I don't consider that a test.)

Safety tips: Never plug a heater in until it matches tank temperature.
Never remove a heater from water immediately after unplugging it. Wait 20 minutes.
Never plug a heater in when you will not be at home to be sure it turns itself off.
If you see water inside the glass tube, unplug the heater. Wait 20 minutes before removing it from the aquarium.
More heater tips can be found in Keeping Murphy Out of Your Aquarium.