Stainless steel heater - prevents the garden pond from freezing (down to -20°). A garden pond should never freeze over completely. The EHEIM anti-ice heater prevents the pond from freezing completely down to -20°C, allowing fermentation gases to escape. This allows vital gas exchange to take place at the surface of the tank. Biological self-cleaning and detoxification of the pond water remain unchanged. As a result, fish and micro-organisms are supplied with oxygen.