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Controlling Algae

The most common problem experienced by pond owners is algae. Of all the technical questions we are asked, questions about algae in the pond is far and away the most common topic. So let’s take a look at pond algae and the best ways to deal with it.

What is algae?


Pond algae may be the floating single-celled variety that turns the pond water into pea green soup. String algae is usually first found in your waterfall or around the pond edges. Unchecked, string algae may take over the majority of your water garden.
Algae is really nothing more than an aquatic plant. It thrives on excess nutrients in the pond water and sunlight. Take one or both of those away, and pond algae is easily controlled.
Excess nutrients can come from many sources. Uneaten fish food, decaying plant matter, fish waste and leaves and other organic debris that may blow into the pond all can cause nutrient levels to increase. In a balanced water garden, aquatic plants absorb almost all of the nutrients leaving no fuel for pond algae. The key to controlling algae in ponds and water gardens is to have enough aquatic plants and the right type of aquatic plants.
Floating plants, such as water lettuce, water hyacinth, water are excellent at absorbing nutrients and providing shade for the pond water to reduce the sunlight reaching the pond water. Water lilies and lotus are great at producing shade, but don’t help much with nutrient reduction. Marginal aquatic plants along the pond edge help in reducing nutrient levels and may help a little with shading. Submerged aquatic plants are the best at absorbing nutrients and are a must for any pond.
String algae and green water problems are common in the early spring when the pond water temperature warms. The pond fish return from being dormant all winter and begin to eat and produce waste. Organic debris on the pond bottom begins to be broken down by bacteria producing more nutrients in the pond water. As the nutrient levels continue to rise, most of the pond’s aquatic plants may still be dormant or just beginning to come back to life. Algae begins to grow at a rapid rate temporally until the pond’s aquatic plants return to prominence. You can help lower nutrient levels during this time by physically removing debris from the pond bottom and abstaining from feeding your pond fish until the water garden becomes balanced again.
Other Ways to Control Garden Pond Algae
An Ultraviolet clarifier is best way to control single-cell floating algae. This device is plumbed inline between the pond pump and pond filter. As the pond water is pumped through the ultraviolet clarifier, the algae cells in the water are altered so that they stick together and cannot reproduce. The algae cells are then removed by the pond filter or sink to the pond bottom where bacteria consume them. Ultraviolet clarifiers are completely ineffective for string algae as the string algae never passes through the UV Clarifier.
EPA registered algaecides are very effective at controlling string algae. Oxidizing algaecides, such as CrystalClear Algae-Off, work upon contact by removing algae directly from rocks and the pond bottom. Algaecides, such as Pond Care AlgaeFix, work over time to kill string algae- usually within a week. We use both products and both have been proven to work every time. Liquid treatments may claim to control single-cell algae that causes green pond water, but we have had very little success using them for this application.
Other products that have not been registered by the EPA as algaecides can be very effective at algae control as well. The EPA is very sensitive that any product that claims to control, kill or eliminate algae must be registered as such. A very hefty fine will be levied against any manufacturer who does not comply, and several in the water garden industry have learned that painful lesson firsthand. The EPA approval process is rumored by cost manufacturers in excess of $250,000 for each product they register. This cost deters many manufacturers from listing products that are very effective in algae control from going through the EPA registration process.