Click 'Read More' down on the right to learn how the pros deal with string algae...
String algae is part of nature, and it does serve an important function. It is an effective bio-filter, and like clams or mussels, it purifies the water where it lives. Unlike clams or mussels, it also acts as a mechanical filter, straining the water that passes through it and capturing some of the silt and debris that would otherwise cloud your water. Another function of string algae is as a food source for many of the animals that live in your pond. Not only will various animals use it for sustenance, they can also use it for shade and shelter. Frogs like to lay their eggs near string algae to keep the tadpoles hidden from predators. The same goes for small fish and some species of insects. Despite these benefits, it can still be a nuisance for pond owners when it grows out of control.
One way to combat string algae is with the use of an Autodoser. This is a tool designed to release a slow and steady stream of a prescribed water treatment at the proper rate for your pond. There are a variety of treatments available for use with an Autodoser, each designed for specific occasions. The one we recommend for controlling string algae is called Maintain for Ponds, this mixture contains a combination of beneficial bacteria, enzymes, and a powerful phosphate binder to reduce pond maintenance and maintain crystal-clear water quality. Other treatments for the Autodoser are useful for breaking down sludge and organic debris, for safely and gently clearing discolored water, and for promoting fish health and reducing stress after a clean-out, but the Maintain treatment is easily the most popular and we have seen excellent results in ponds treated with it.
Dosing your pond with bacteria and enzymes is a valuable preventative measure when battling string algae. The bacteria consumes nutrients in the pond that would otherwise sit dormant as sludge, like an all-you-can-eat buffet for algae. To really make a difference you'll want to combine these treatments with some good ol' manpower.
Despite advances in pond science and innovative new products, the most effective way to quickly clear string algae from your pond is still the old-fashioned method of pulling it out by hand. This removal method will eliminate the bulk of the algae from the water, and prevent it from breaking down into nutrient-filled sludge that would otherwise fuel a new round of algae growth.
A long-handled brush can be useful for reaching the deeper parts of your pond, and for retrieving string algae that is in less accessible areas. Depending on the size of your pond, you may have to wade into the water to get to all of it. A long handle to hold can serve double purpose in this scenario, helping you keep your balance on wet, slippery rocks.
We generally avoid the use of algaecide in our ponds. It does not treat the cause of algae, which is excess nutrients, it just kills off the existing algae, which only adds to the nutrient load in the pond. As you might imagine, that would lead to an even larger algae bloom next time, which could be as soon as a week or two later. The one time we might make an exception is in a pondless waterfall system without any fish. In those cases, after scrubbing with a brush and removing whatever algae we can get by hand, we would shut off the waterfall pump for about 15 minutes and apply EcoBlast / Rock & Waterfall Cleaner to affected areas where the string algae is anchored to the pond. This stuff is most useful when the algae has covered entire rocks and it has become impractical to remove it all by hand.
Once you've cleaned the algae from your pond and have applied treatments to restore the balance of the ecosystem, you should consider whether your pond has enough plants. This is perhaps the single most important consideration when it comes to finding harmony in your pond. The right amount of plants depends on how much nutrients your pond is producing and accumulating. Not enough plants to convert those nutrients into foliage and flowers is a guaranteed way to develop an algae problem. If you have a lot of fish, they will be making lots of fertilizer, and you'll want more plants. If your pond is downhill from manicured lawns and landscapes, there is a possibility it collects runoff fertilizer. If so, you'll probably need more plants to account for the additional nutrients in the fertilizers, but if it's really bad you may want to consider redesigning the pond or surrounding landscape to redirect the drainage away from the pond.
There are two more tools that are often used with the intention of eliminating algae: the UV Clarifier, and the copper IonGen. These each have a specific function in the pond, and can be quite helpful when used correctly. It is important to understand how these tools work, because if they are used incorrectly they can create their own problems in the aquatic ecosystem.
First, we'll discuss the UV Clarifier. This tool is great for eliminating the green water that occurs with pea-soup (planktonic) algae blooms. The UltraKlear UV Clarifier is basically a section of plumbing with a sleeve containing a T5 high-output UVC bulb. The ultraviolet light emitted by this unit sterilizes the water passing over it, killing any single-celled algae. It does a great job at preventing green water, but because it only treats the water passing through the sleeve, it's not effective against the multi-celled string algae that is rooted to the rocks or plants in your pond.