How to Keep String Algae Out of My Pond

String algae grows in ponds exposed to excessive sunlight and leftover nutrients from decaying plant or fish waste. This combination provides ideal conditions for algal spores to develop and take over your pond, choking plants and clogging your filter. Most types of pond algae remain dormant throughout winter and flourish in spring when conditions become favorable for growth. Treat established algae colonies with a chemical algaecide or natural barley straw solution, or remove the causes of algae from your pond in early spring to prevent an outbreak of slime in summer, when your pond should be at its best.

Things You'll Need

  • Pond net or rake
  • Chemical algae inhibitor
  • Concentrated barley straw extract
  • Watering can
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Instructions

  1. Prevention

    • 1

      Remove decomposing leaves and plants from your pond in early spring before algal spores have a chance to take hold. Garden debris blows into your pond in winter and breaks down, releasing nutrients into the water and allowing algae to bloom. After your initial spring clean, check for waste plant matter once a week, and remove debris with a pond net or rake to stop further build-up. Regular seasonal pond maintenance keeps water healthy year-round.

    • 2

      Maintain appropriate fish stock levels for the size of your pond. If you are not sure how many fish your pond and filter can deal with effectively, use an online fish stock calculator. Type in your pond dimensions and filter specifications, and the calculator will advise the maximum number of fish in your chosen species that the pond and filter can handle. If your pond has too many fish, the filter will be unable to operate efficiently, and excess waste will remain in the water, providing algae spores with the required nutrients to grow.

    • 3

      Introduce frogs or toads to your pond. Amphibians rarely need much in the way of an invitation to move to an established pond, so maintain healthy water to entice local species into your garden naturally. Tadpoles feed on string algae, and although a group of baby frogs is unlikely to consume a pond full of algae, they will nibble at new growth and help keep levels down in conjunction with other methods.

    • 4

      Install an ultraviolet filter to help prevent string algae regrowth or treat an existing problem. UV light kills algae at the spore stage and effectively keeps string algae under control.

    Treatment

    • 5

      Scoop loose algae from the pond surface using a pond rake or net, and pull out as much as you can from below the surface. Treatments work most effectively if you net out clumps and strings of established algae before dosing the pond.

    • 6

      Choose a chemical algaecide or natural barley straw liquid solution. Calculate the volume of your pond using a pond calculator, and prepare the correct dosage of pond treatment. Mix the algaecide or barley straw solution in a watering can according to the manufacturer's instructions, and pour the solution over the pond surface.

    • 7

      Reduce or stop feeding your fish for a day or two if string algae is growing out of control, because this is an indicator of excess waste in the water. If the waste is from uneaten food, cut back feeding the fish to every other day. Deprive spores of nutrients and they are unable to survive.

    • 8

      Add preventative doses of your chosen pond treatment to stop summer regrowth, and net out any debris as it falls into your pond so it does not have an opportunity to decompose.