In aquatic environments, the temperature matters...a lot! All of the inhabitants living in our pond or aquarium are cold blooded. Plants, fish, bacteria, algae, snails, corals, and the rest their temperature is the water temperature. Their metabolic rate is determined by water temperature. This is one of the key differences between aquarium pets and our other family pets. For example, we don't stop feeding our dog when the snow starts to fall, but we do stop feeding the pond fish.

Most common aquarium species are tropical fish. They come from areas where the water stays relatively warm all year round. That fact is pretty convenient for aquarium owners. We can use a heater to keep the aquarium a few degrees warmer than our home relatively easily. Coldwater fish, like koi, are naturally better adapted to the wider seasonal temperature changes in your pond. However, they don't always tolerate tropical temperatures well. Aquarium fish generally do best within a stable temperature range. 76-78 F is a good range for lots of tropical fish. Unless you keep the room where the aquarium is 78 F all the time, you probably need a heater in your aquarium.

Just because you can set the thermostat on your heater, you still need a thermometer to measure the temperature! Unfortunately, heaters can fail. They can get unplugged or even get stuck on heat. That's bad! Avoid using an oversized heater. For aquariums larger than 60 gallons, it's good to use two smaller heaters set to the same temperature. If one dies, usually the other keeps the temperature safe. For most home aquariums, 3-5 watts per gallon is the simple rule of thumb.For example: A 29 gallon tank would need a 100-150 watt heater.

Learn a great habit. Check the temperature every time you feed the fish. Get a nice thermometer that you don't want to hide. Digital thermometers are easy to read. The ones that store the minimum and maximum temperature are really useful, that way you can see how far the temperature varies each day or each week.

Higher temperature means less dissolved oxygen is available in the water for your fish. Their metabolism increases, but there is less oxygen available to support their metabolism. Check the heater for proper function and reduce the setting. Filter pumps and aquarium lights may be warming the water too much or the tank may be located in a warm area in your home.In a high temperature emergency, turn off the lights and unplug the heater temporarily. A partial water change using cooler water to drop the temperature 2-4 degrees should help your fish right away. Maximize aeration of the water.

Aquariums with high light needs can easily overheat, especially on days when the room temperature jumps up a few degrees. These aquariums may require an aquarium chiller system.

If the temperature is too low, check for heater malfunction. Your fish may seem sluggish and have poor appetite.If the heater is working, turn it up. Use a heater (or heaters) rated for your aquarium volume. The aquarium may be located in a cool area and require a larger heater or an additional heater.