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Treating ponds in winter. – Pond & Lake Q & A

Algae tends to grow all year long – even in cold temperatures when ice covers your pond.

Pond & Lake Q & A

Q: The weather is getting colder, so can I still treat my pond with chemicals or natural bacteria? – Sara in Washington

A: Algae tends to grow all year long – even in cold temperatures when ice covers your pond. Given the right mix of nutrients, carbon dioxide and sunlight, these little photosynthetic, autotrophic compounds will flourish – regardless of the temperature or time of year.

Whether you can treat the pea soup or filamentous algae depends on the water temperature in your lake or farm pond. When the underwater thermometer drops below 50 degrees Fahrenheit, the effectiveness of both chemicals and natural bacteria begins to drop. So to get the most for your money, we recommend dosing your pond or lake with one of these methods in the fall before the winter chill hits:

    Treat with Chemicals: As long as your water temperature is about 60 degrees F, you can use algaecides, like Algae Defense® (or Clipper™ if you have koi or goldfish in your pond), to help with late-season algae blooms. Warning: If your lake is stocked with trout, test your carbonate hardness before adding Algae Defense®. If your Water Hardness Test Kit reads less than 50 parts per million (2.79 degrees of hardness), it could be toxic.
    Add Some Shade: Regardless of your water temperature, you can also add pond dye to shade your pond or lake during the winter. Throughout the pond industry, experts use dye to minimize the amount of sunlight that reaches the depths of ponds and lakes. This can prevent algae from photosynthesizing – and limit its growth.
    Treat Naturally: Beneficial bacteria, like PondClear™ , are also most effective when temperatures are above 50 degrees F. When used correctly, they will help to keep your pond crystal clear.

POND TALK: Have you experienced a late-season algae bloom in your lake or pond? What did you do to control it?

11 Responses

  1. i run a skating pond in new jersey we had a week of warm weather and now half of our pond is cover in algae that is in the ice. do you have any ideas for me?

    • Hi John,

      If the ice is off the pond at the moment you could physically remove the algae with a rake that would be able to pull algae from the pond. Normally I would reccomend treating the algae before raking but while water temperatures are still below freezing you won’t be able to do any treatments to the pond. The best thing would be to plan a maintenance program for the pond this coming season with natural bacteria and aeration to reduce the buildup of organic material in the bottom of the pond. Since you do use the pond in the winter you will want to remove the aerator for the winter months, however aeration throughout the summer will help for a healthier pond in the winter. Good Luck.

  2. I’m really interested in Pond Water Features, as I’m growing increasingly keen in wildlife and habitats so I’ve recently purchased my pond supples from UK Water Features. I’m fairly new to all this. So when would be the best time to construct a pond, and also I live in a hard water area and what effect will this have on the Pondlife?



    • Hi Jayne,

      Water features are a great addition to any landscape! Spring construction is probably the most beneficial because your pond and filter can cycle and get established before the coming summer months and you will get to enjoy your new feature all year. Hard water may have some affect on fish and plants but we have a product called Pond & Fish Conditioner to solve that particular issue. This product can condition the water making it safe for your fish and reducing the water hardness. You may also want to look into our Pond Logic Defense Pac. The package deal contains natural bacteria and cleaners to aid in pond maintenance all season long. You also mentioned you purchased a kit for construction. If this uses a waterfall basin for the filter system be sure you have adequate filter media, many basins come with 2 filter mats and a media bag but you will need to purchase the additional media for the bag in order to receive full benefit from your filter. Please click on the above product names to view more information on our website. I hope this gives you a good idea on where to start!

  3. I plan to draw down the level of water in my pond soon. I was told that this will freeze the weeds and kill them around the perimeter of the pond. The draw down will be about 2 feet of a 10 foot deep pond. Its dimensions are about 50 feet wide by 100 feet long and is oval shaped. This procedure is supposed to create a better looking shore line next year. Will the draw down kill hibernating aquatic life like frogs, turtles, etc.? Also, will it be harmful to fish?


    • Hi Ben,

      Early fall would be the recommended time to draw down your pond to leave plant roots, such as Cattails, exposed to winter’s coldest temperatures. This will help reduce the amount of plants that reemerge in the spring; it will also allow you to chemically treat what does emerge. At this time of year, turtles and frogs would not have started to go into hibernation. Once late fall arrives and they have begun hibernating, reducing the water level would make them vulnerable to die from exposure.

      You could deplete oxygen levels in the pond if the water levels are dropped too low — especially if the pond does not have aeration. If you have an aeration unit running in the pond year round, such as a bottom-bubbler, the oxygen concentration in the pond would not be an issue for your fish.

      • I am considering buying a bottom-bubbler for my pond. The location for the Airmax compressor might be next to my house where I could run an electrical extension. Does the compressor make a lot of noise, like in comparison to a refrigerator?


  4. Why would you have to add dye, if you have several good snowfalls, Wouldn’t that be good enough to cover the pond from the sunlight?

    • Hi Christine,
      If you could rely on the snow remaining on the ice all winter, this might be true. However, with wind blowing the snow off, temperature warm-ups and rain melting the snow throughout the winter, you cannot be sure that you will have sunlight blocked from your pond. It’s better to add dye than worry about it during the winter months.

  5. What do you do about string algae when the water is below 50 degrees? Since the water has cooled here in Chicago, I have stopped using bacteria and am having an algae bloom!

    • Hi Paula,
      In some cases, a pond that stays clean and clear through the summer can blow up into an algae nightmare in the fall. Shutting down your water garden ceases the flow-through characteristics of the pond. This reduces the amount of filtration that occurs both mechanically (skimmers) and biologically (filter falls). Since there is less flow, it’s a good idea to bump up the amount of bacteria in the pond by adding Seasonal Defense® Bacteria with Barley. These bacteria operate in cooler conditions and will greatly reduce the amount of nutrients in the water; they also contain barley straw to naturally help with algae. Also, using Oxy-Lift™ Defense® to scrub down your rocks will help remove any debris build up.

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