Heating and Lighting Thermometers for Pets Fish are essential for creating the perfect environment for your fish. They help you to keep the temperature of the water in the tank at the right level and also help to create the right lighting conditions for your fish to thrive. There are a variety of heating and lighting thermometers available, from digital ones with LCD displays to more traditional analogue models. They come in different shapes and sizes to suit different tanks and aquariums, so you can find the perfect one for your fish. Some thermometers also have additional features such as alarms and timers, so you can easily monitor and adjust the temperature of your tank.