A Pond De icer or Floating Pond De icer will keep your pond de iced leaving a hole in the ice for gas exchange. In areas with extreme weather conditions where your pond may completely ice over, decomposing organic matter such as leaf debris at the bottom of your pond can generate dangerous gases. Without a hole in the ice these gases will remain trapped in the pond water and can cause a fish kill. That is why it is so important to provide a small opening in the ice on the top of your pond with a Floating Pond De icer.