Aquatic Connections recommends doing a water change before winter. Pond water that is balanced and clean will promote better fish health as the water temperatures get colder. Stress Coat should be added to help reduce the stress koi and goldfish experience when pond water is changed or the fish are moved from their environment. Stress Coat replaces the koi and goldfish's natural slime coat. Click here to get more information on Stress Coat, a Pond Care Product by Mars FishCare.