As you know, fish from tropical and subtropical waters need a certain constant water temperature. Before the engineer Eugen Jäger invented the aquarium controller heater decades ago, there was no really satisfying solution to generate the right water temperature for the species. The methods used were complicated and sometimes curious. Some placed the aquarium in the sun or on the heater or oven. The Eheim aquarium controller heater is a further development of the legendary heating rod. The temperature can be precisely set from 18 to 34 °C and readjusted if necessary (±2°). The control accuracy is ± 0.5 °C. The heat is kept constant. A control lamp indicates the heating function. The rod is absolutely waterproof, can be fully immersed, has Thermo Safety Control and is suitable for fresh and salt water. One of the most important innovations is the glass jacket: it enlarges the heating surface, compresses the heat, ensures optimum, uniform heat dissipation and forms a heat shield (the aquarium inhabitants don't mind touching). The jacket is made of special laboratory glass. This was created for research purposes. It is therefore free of pollutants that could be released into the water. Chemical and biological substances do not attack it. There are no fissures or hairline cracks through which condensation water could pass. It's impact resistant. And even extreme temperature fluctuations, such as may occur when changing water, do not bother this glass.