How to Read a Temperature Strip on an Aquarium

Keeping fish healthy in an aquarium is no small task. You have to keep the aquarium clean, ensure it has the proper salinity, be sure your fish have enough food (though not too much), maintain the right PH levels, and keep it at the right temperature. While there are a lot of thermometer options available for fish tanks, the adhesive, stick-on thermometer strips are the cheapest and easiest to use, although they might not be the easiest to read.

Goldfish in an aquarium
How to Read a Temperature Strip on an Aquarium
credit: Kameleon007/iStock/GettyImages

Installing stick-on thermometer strips

Installing a fish tank temperature sticker is easy. The website Pets on mom.me says the thermometer can be installed on the side, front, or back of the tank (ideally somewhere that will not obscure your view of the fish in the tank), but you must clean the area first. Simply wipe down the outside of the tank with glass cleaner and a soft, lint-free cloth. Next, peel the adhesive off the thermometer strip and line the strip up to the glass without touching the two together to ensure it is put on straight. Once the strip is straight, press it against the glass. Finally, use the side of a credit card to smooth out any bubbles under the sticker. The sticker should be ready to use about 30 minutes after installation, according to Fish Tank Club.

Reading your temperature strip

You may not have any trouble installing your aquarium thermometer sticker, but how to read it is another matter. These thermometers usually have one side in Fahrenheit and the other in Celsius. While some strips operate similar to a traditional mercury thermometer with a red line going up the middle, most have a rainbow of colors that will move up and down the thermometer based on the temperature and give you a range of temperatures.

The blue/violet part of the rainbow reflects a temperature below the tank's actual temperature. The red/orange colors show a temperature above the exact temperature. The real temperature of the tank will be right around the middle of the rainbow, usually in the green area. For example, if the blues and purples are at 84 degrees, the green is at 86 degrees, and the red is at 90 degrees, then the temperature is probably closest to 86 degrees.

Problems with thermometer stickers

Thermometer stickers might be inexpensive (starting at only $2) and easy to install, but they are still the least preferable of all fish tank thermometers. That is because they are located on the outside of the tank, which means they cannot possibly be as accurate as an in-tank thermometer since the temperature of the room will affect the reading.

In order to make a stick-on fish tank thermometer as accurate as possible, Starting an Aquarium suggests making sure there is no direct sunlight falling on the strip and that it is not right next to a heating or cooling source such as a furnace, fireplace, air conditioner vent, swamp cooler, etc. These can make the already-inaccurate strips wildly unreliable, and if you act (or fail to act) according to these readings, you could put your fish at risk. This is why it is advisable to use a submerged thermometer instead.

If you like thermometer strips, you can always choose to put one on the outside of the tank and then double check one in the tank if you think the temperature is getting too hot or cold for your fish.