A properly lined pond won’t lose or gain water through the ground, creating a stable environment that is easy to keep within the right parameters. Most fish kept or raised in ponds need a specific pH range and oxygen levels. They’ll still need the same conditions over the winter, but it can be tricky to both test and treat water when it’s cold and covered in ice. Shutting off pumps and aerators to keep them from freezing also makes it harder to circulate treatments to change the pH or treat high nitrate levels. Keep water quality levels steady over the winter to minimize the need to test or treat with these tips.
Leave Openings for Air
The single most important factor in water quality, over the winter, is the amount of ice allowed to form over the top of the pond. A complete cap of ice traps gases that would normally evaporate, concentrating them in dissolved form in the water. Ammonia, carbon dioxide, and other natural by-products of waste breakdown need to escape rather than remain trapped in the water. Don’t tightly cover a pond with an impermeable cover for more than a few hours. Install de-icing equipment in the pond and check it regularly throughout the winter. Even a few hours of complete ice cover can hurt sensitive fish, so don’t let your de-icing units fail or become disconnected from their power source.
Avoid Feeding the Fish
It’s tempting to toss in some fish food when the weather temporarily warms up in the winter. The fish visiting the holes in the ice or swimming along the surface may look hungry as they gulp in air. However, they’re still dormant enough that they don’t need to eat. Adding in food, even fall and spring feed, could disrupt the water quality balance when there’s little bacterial activity to break it down. Even when the fish do eat all the feed you give them, their extra waste still throws everything out of balance. Leave your fish without any meals when temperatures are below 39 degrees F. Only start feeding fall and spring feed when temperatures are consistently above that threshold for a week or more at a time, and unlikely to drop again.
Minimize Plant Debris
Cleaning the pond before winter, with a specific focus on plant debris that’s grown or fallen in the pond, is essential for water quality maintenance. In a pond with no fish or frog life, you’re free to let debris build up until it’s interfering with the desired depth. Fishponds tend to skew to the acidic side of the pH spectrum and develop slow nitrate conversion rates when too much organic material builds up. Cutting out unnecessary plant growth, that’s not going to survive the winter, is essential to prevent a sudden burst of material from entering the ecosystem as frosts kill leaves and stems. Take some scissors or a pole-handled pruner and rake to remove what’s unnecessary. You’ll see strong growth to replace what’s pruned out when spring arrives the next year.
Clean Filters
Some pond owners shut down and drain their filtration systems without cleaning or removing the filters inside. They reason that they can just clean them in the spring before restarting the system. However, water can still flush through the filtration system temporarily and drain effluent from the dirty filter back into the pond. The filter will also be harder to clean after the debris on it freezes and thaws dozens of times over the winter. Clean your filters thoroughly, even biofilters and sand basins, to make sure they’re ready for the spring and won’t cause winter water quality issues.
Consider an Aerator or Submersible Pump
Oxygen levels can drop suddenly in the water enclosed under a thick layer of ice. Even if you’ve left multiple holes with de-icing heaters, it’s not easy for the oxygen to mix into the water in the winter. Aerators and submersible pumps increase circulation when the water is too cold to naturally mix and move. Most fish don’t need these devices because they’re dormant and use little oxygen, but ponds with water quality issues over the winter may require pumping or aeration to keep gases balanced.
Most pH and water quality tests operate within specific temperature parameters, so you’ll likely need to take your pond water samples indoors to warm them before testing. Don’t forget to test the water quality occasionally. It’s unlikely to change much over the winter due to the slower action of bacteria in the pond, but sudden changes can occur on warm days.
