Dead leaves, algae, insects and solid fish waste that have accumulated over the summer slowly break down during the winter months. This natural decomposition uses oxygen and produces small amounts of hydrogen sulfide, a toxic gas that normally never reaches a harmful level. Fish, frogs and other aquatic life are especially sensitive to poor water quality in winter. A build-up of leaves and other organic matter can cause an imbalance, reducing oxygen to dangerously low levels and releasing poisonous hydrogen sulfide. Click here to read more about Winterizing your pond from Pond Care
