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All, Summer

Algae & The Water Garden

August 31, 2021

Algae The Water Garden

Algae & The Water Garden

All water gardens have algae but too much algae can cause the water to become cloudy and turn green. Water naturally contains many elements, mineral salts, and nitrates. When sunlight hits the water, the temperature increases and evaporation takes place. The mineral salts and nitrates are left behind, and the water is 100% pure. This is compounded every time more water is added.

Algae feed on the salts and nitrates and proliferate when concentrations are increased. Algae also feeds on the dissolved nutrients of decaying debris like dying aquatic plant foliage or leaves that fall into the water. If you have a large fish population, this could be an added reason for algae in your pond as their waste breaks down into nitrate fertilizer.


Water Plants will absorb salts, nitrates, and dissolved nutrients of decaying organic matter in the pond. To create a natural balance and maintain clear water, try to have some from each of the four types:

  • Oxygenating Plants – Cabomba, Elodea, Hornwort, Sagittaria, and Vallisneria grow under water just like the plants you see growing in naturally occurring ponds and lakes. They absorb excess nutrients from the water that cause algae. They also liberate oxygen, provide spawning space for fish, as well as shelter and protection for baby fish. Use one bunch per 2-3 square feet of open surface area (less will be required for small ponds).
  • Floating Plants – Water Hyacinth, Water Lettuce, Duckweed, Salvinia, and the floating leaves of Water Lilies help to shade the water thereby reducing evaporation so that you won’t need to continually add more water. At the same time, the water stays cooler creating a healthier environment for plants and fish.
  • Marginal Plants – remove a lot of the nutrients that algae would normally feed on. Consider hardy Pickerel Rush, Variegated Sweet Flag, Yellow Water Iris, Corkscrew Rush, Cattail, or tropicals such as Canna, Taro, and Papyrus to make the edge of your water garden more attractive and help to keep the water clear.
  • Water Lilies – available in two forms; hardy which can be cut back and left in your water garden over the winter, and tropical which you would treat as annuals or lift and winter inside. The significant visual difference between them is that hardy Water Lilies have their bloom on the surface of the water with the foliage while tropical blossoms rise on long stems well above the leaves. Both are easy to grow – they require only 6 hours of sunlight per day, rich soil, and calm water. Hardy Water Lilies bloom yellow, red, apricot, white, and pink. Tropicals are white, pink, red, yellow, purple-violet, and blue.

Snails – a beneficial addition to your eco-system. Snails feed on the algae that sticks to the side of your pond and submerged plant containers.

Fish – will eat some algae, mosquitoes and other insect larvae. Be sure you have the right number of fish appropriate for your pond size. Stock 2.5 cm of mature fish per one square foot of pond surface area. Do not over feed your fish as the algae thrive on decomposing fish food. Feed fish only what they can consume within the first few minutes.


The two basic types of filters are mechanical and biological. The idea behind them is to circulate the total volume of water through a filtering system once every 1 to 2 hours.

  • Mechanical Filters – a simple mesh or screen device that traps floating debris. Attach this to the pump inlet to keep foreign objects, fish, snails, and tadpoles from getting into the pump. Many biomechanical filters also include a sponge or mesh pre-filter. Keep your filter clean and replace once a year.
  • Biological Filters – uses bio-balls, plastic mesh, beads, or lava rock to filter suspended solids and support beneficial bacteria that absorb excess nutrients and chemicals. Any disturbance agitates the beneficial bacteria. A skimmer is best installed at the far end of the pond from the waterfall or stream. The pump is placed inside so that it sucks any leaves or other floating matter into the skimmer. This prevents anything falling to the bottom of the water garden that Be sure to check, empty and clean the skimmer often.
  • Ultraviolet Filters – helps to eliminate green water. Ultraviolet radiation makes single-celled algae clump together. In a larger mass, algae can be removed easier with the all-purpose pond filter.

Pond Shade is a blue-tinted liquid that filters sunlight to reduce algae and cool the water. Safe for all aquatic plants and fish. Follow package directions to avoid too much shade on the pond


Place barley straw in the pond shortly after the ice melts to prevent string algae. As the straw decomposes, it converts to hydrogen peroxide. If kept at consistently low levels the algae growth will be inhibited. You can purchase barley straw in a mesh bag with an attached string. Anchor the bag so that it floats on the surface, in or near moving water. Each bag should last approximately 6 months. Your pond water will likely turn green in the spring before your plants have a chance to grow and cover the surface. If this persists, add more plants or get rid of a few fish.

*Do not ever completely empty the water from your pond and start again. This will shock your fish and will take longer to create a natural balance.