Winter pond care for koi requires two main approaches for the best outcome. Koi are very hardy fish, they can survive water temperatures as low as 0°C, which means they can survive in a pond during winter, provided it doesn’t freeze solid, that they have adequate water quality and oxygen. 
The best way to ensure that your Koi have an adequate oxygen supply and water quality as well as preventing freezing is with a SAS or Canadian Air System (depending upon depth and size) and ensuring you have applied a Fall Dose of Equinox Bacterius Bacterial conditioner. Bacterius® EQUINOX was developed to biodegrade cellulose material generated from dead leaves in autumn. Bacterius® EQUINOX rapidly colonizes in the muck and quickly prevents the proliferation of sulfate-reducing bacteria that are responsible for H2S that contributes to anoxic conditions. H2S is a toxic gas that causes unpleasant odours (rotten egg smell) and deterioration of bacterial biofilms.
With an application of Equinox and a proper aeration system you can be assured that your Pond and your Koi and other pond life will make it through the winter. Bacterial conditioners like Equinox are made as much as 3 times as effective with the correct size aeration system, ensuring H2S gasses, decaying plant matter, fish waste, and algae are digested and broken down over the winter. This will ensure your pond has a head start in the spring. That means less maintenance, and clearer cleaner water.
