High-quality heating wires and 2 mm thickened corrosion-resistant quartz glass, suitable for fresh water and saltwater tanks. With suction cups, easy to fix the heaters in fish tank firmly, no complicated installation steps, convenient and quick for use. With red indicator lights on both sides, which will be on when powered, easy to know working state. The thermometer sticker has a range of 39℉ to 97℉ and 4℃ to 36℃, and the temperature sticker is a temperature-sensitive paper with color-coded markings showing the current temperature, which is very easy to read. Please choose right heater power and quantity according to actual tank capacity and different temperature. Heating speed depends on the size of fish tank, but installing it close to the circulation pump or filter will help to disparate heat so that the whole tank can warm up quickly.