Algicides to Kill String Algae & Hair Algae

Garden ponds develop string or hair algae when sunlight and excess nutrients in the water feed dormant algae spores during the spring. Algae can double in volume on a hot summer day, clogging your filter and smothering plants. Different types of algicide kill algae in different ways, and you can choose natural, chemical, shading or flocculent products, depending on your type of pond and its contents. Calculate the volume of your pond accurately using a pond calculator, before administering an algicide treatment.

  1. Natural Algicides

    • Algicides containing barley straw are safe for most domestic garden pond setups. Barley straw is a natural plant-based algicide and poses no threat to pond plants or fish, including koi. Powders and liquid solutions contain activated or concentrated barley straw extract, or you can place a tied bunch of barley straw beneath a pond rock for an alternative natural algicide that works in harmony with your pond's ecosystem. Remove dead algae as soon as it turns brown, and before it decomposes completely, because rotting algae will contaminate your water.

    Chemical Algicides

    • Copper-based chemical algicides quickly eradicate string and hair algae, but they can be harmful to fish and plants. Koi are highly sensitive to copper, so check the warnings on your chosen brand of algicide before using it in a koi fish pond. Use chemical algae treatments with caution around children and pets, and choose a pet and child-friendly brand. Hedgehogs, frogs, tadpoles and other creatures are also affected by some chemical algicides, so if your pond has a lot of visiting wildlife, you may wish to use a natural solution instead.

    Shading Agents

    • Algae grows best when there is an abundance of natural sunlight. Shading agent algicides effectively take away the sun, and the algae dies. Shading agents contain a colorant that darkens pond water, reducing the amount of sunlight penetrating the water. These products turn the pond water blue or black, and are often unsuitable for fish ponds. Read the manufacturer's guidelines carefully before making a purchase, because shading agents may also leave a color residue on gravel, rocks and plants.

    Flocculents

    • Large clumps of string and hair algae can hang in the water, shedding particles too fine for removal by filtration. Instead, the floating scum causes cloudy or murky green water in addition to patches of algae. A flocculent algicide binds suspended particles together so they are large enough to net out manually, settle to the bottom of the pond or become trapped in the filter. Flocculents work well in conjunction with other products like barley straw, producing effective results and an algae-free pond.