Heaters and Deicers keep pond water safe for your fish during the winter months. As a pond freezes over, toxic gases begin to accumulate underneath the ice, saturating the water. Over time, the build-up of toxic gases becomes harmful or fatal to your fish. The quickest and simplest way of preventing this build-up is by installing a pond de-icer. When used properly, a deicer will heat the water directly around it to a temperature slightly above freezing in order to create a small hole in the ice. This small hole allows toxic gases to escape the water making it safe for your fish. Many heaters and deicers are thermostatically controlled to operate only when the temperature drops below freezing. This saves energy, creating a practical solution to the problem of over-wintering fish.