Some fish and amphibians are extremely sensitive to temperature changes and can suffer or even die when the water is too hot, too cold or fluctuates. An adhesive temperature strip tells you how hot the water is by showing three colors on the thermometer. Because each color indicates a different temperature, anyone who has not worked with a temperature strip may not understand how to read it. One color is the exact temperature, while the other two colors indicate a temperature that's either warmer or cooler than the exact temperature.
Clean the outside of the aquarium with water or with an aquarium-safe glass cleaner. Do not use soap or standard glass cleaner as the chemicals may contaminate your water. Dry the aquarium thoroughly, using a towel. Ensure that the glass is completely dry.
Peel off the plastic backing from the strip. Place the strip on the outside of the tank, below the top water level. Ensure that the strip is smooth and free of bumps.
Look at the strip after about 15 to 30 minutes. You will see three colors, each with a number. Green indicates an exact temperature. Blue or violet indicates a temperature that's below the exact temperature. The red or tan color indicates a temperature above the exact temperature.