Most pond owners really begin to notice algae when it ‘blooms’. By the time you see this amount of growth, it is too late for a preventative, but you do have several control options. The most common reasons ponds have excessive algae are too many fish, decaying organic matter, weather/temperature changes, not enough plants/water cover, and lack of proper filtration/aeration.
Before buying control products, make sure you know what type of algae you have and the main cause. Some algae is healthy and is a necessary part of a balanced pond’s ecosystem. Expect a healthy pond to be free of green water 10 months out of the year.
There are two basic types of algae that can occur in most ponds. 1) Single cell, free-floating algae and 2) string algae. Single cell algae is the most common cause of green water in ponds. Your water garden may go through a “green pea soup” phase before your plants become well established. This is normal, harmless to fish and plants and will clear up as your plants grow and absorb the nutrients the algae needs to survive. Do not drain your garden and put in fresh water, it will just repeat the same green water phase until a balance is reached! Once balanced your pond should remain clear enough to see near the bottom of the garden at least 10-11 months of the year.
To speed clearing of the water add more competition for the algae (more submerged or floating plants), reduce the number or quantity of fish (fish waste is a natural fertilizer for algae) and remove any plant and leaf debris that has collected in the pond. Limiting fish feeding to once or twice a week (if at all) will also help since the fish will forage more thoroughly for other food sources that may otherwise add to the debris in your pond. Make sure any food that is not eaten in 10 minutes is removed. Weekly applications of beneficial bacteria such as Hydro-Bugs or Green-be-Gone can be very effective.
Outside of using applications to control the free-floating algae, a UV sterilizer can be a great resource to have on your side. An ultraviolet light bulb inside an filtration device can be used to do away with microscopic organisms that make up pesky single cell algae. A proper size UV sterilizer with a proper size pump will give you clear water within 1-2 weeks nearly 100% of the time!
We do not recommend the use of any commercial algaecides since they are often detrimental to the eco-balance of your pond. Remember the two most common causes of green water in any pond are: #1) too many fish being fed too often; #2) lack of leaf control in the fall!
The second type of algae you may see is commonly called string algae and grows along the side of the pond, usually attached to rocks, pots, or the liner itself The thin green layer you will see form on rocks and the sides of your garden below water is normal, desirable and a sign of a healthy pond. If string algae becomes excessive, stop feeding your fish and follow the other steps outlined above. It can also be manually removed with a small leaf rake etc., or the addition of some snails such as Trapdoor or Black Ramshorn may be helpful. String algae is most prevalent in the spring and fall during cool weather but normally subsides in the summer. (If string algae continues to be a problem, there are a couple of relatively new products on the market that can help without the risk of hurting your fish or plants. Stop by or give us a call for details).
Finally, keep in mind that algae is a people problem - the fish don’t care! After all, how many ponds do you see with crystal clear water? We’re just trying to tweak mother nature just a little so we can see all the beautiful residents of our little piece of watery paradise!
Algae in ponds can vary tremendously based on fish load, biological filtration and other factors. For reference here is a chart offering solutions and explanations for solving your algae problem: