Aquarium Heaters

for the week of 9/10/98

Every year when the weather turns cooler, we begin to receive calls from customers who have sudden outbreaks of “ich” or other disease, or lose fish for no apparent reason. Often, we find these problems to be caused by temperature fluctuations that could have been prevented by a good aquarium heater. As cold-blooded animals, fish are very sensitive to changes in water temperature: a few degrees drop in a 24 hour period can lower their resistance to common infections like “ich;” a larger drop can kill some fish outright.

Selecting a good heater. Heaters vary considerably in price, performance and features. Low-priced models (about $10) generally have poorer quality thermostats, and do not keep the temperature as stable as mid- or higher-priced units – even when new. And as they get older, they become even less reliable. Mid-price heaters (about $15-$20) generally perform adequately for most tanks and have a somewhat longer functional life than low-priced models. The best heaters (about $30-35) generally have more accurate, longer-lasting thermostats, and often include extra features like submersibility and easy-set temperature markings.

Getting the right size. For our Wisconsin climate, a good rule of thumb is to allow about 5 watts per gallon for tanks up to 30 gallons, and 3-4 watts per gallon on larger aquariums. As such, a 30 gallon tanks would typically use a 150 watt heater (30 gallons x 5 watts) and a 55 gallon might use a 200 watt. Too small a heater may lead to chilling on cold nights, while too large a heater could lead to “boiled fish” – especially if the heater is of poor quality or getting old.

Heater Placement. Water current ditributes heat, so place the heater near an outside power filter, water pump, or aerating device. This will not only prevent hot and cool spots in the aquarium, but will also extend the life of the heater by reducing the number of times the thermostat kicks on or off.

Check Temperature Regularly. Even the best, most expensive heater doesn’t last forever. As the thermostat wears, tank temperatures begin to fluctuate more and more drastically. Finally, the thermostat may “stick,” causing the heater to remain on and raise the temperature well beyond the safe range. If a stable tank temperature gets harder and harder to maintain, it may be time to replace the heater.

“Tip of the week” appeared regularly in 1999 and 2000.