A common problem that many pond keepers experience is the growth and expansion of pond string algae. Sometimes also called hair algae, blanket algae or blanket weed, this pesky form of algae flourishes in warm water and has an uncanny ability to clog drains, filters and pumps because of it's 'stringy' nature. During the day, string algae undergoes photosynthesis much like other plants which introduces oxygen bubbles into the algae mass, which is what causes it to float to the surface of the pond. At night, hair algae then undergoes respiration, which uses oxygen and produces carbon dioxide as a byproduct. Since the beneficial bacteria in a biological filter also use oxygen as part of the process of converting ammonia into nitrate, blanket weed can help contribute to low oxygen and high ammonia levels in a pond.
String algae shouldn't be confused with other forms of algae found in a pond. For example, the algae that creates green pond water is not string alge. Furthermore, the soft gelly like substance found on rocks near the edge of a pond is also not string algae. String algae is characterized by its long, stringy nature and its ability to wrap around objects and 'hang' off rocks and waterfalls.
While it is difficult to permanently remove blanket weed indefinitely from a pond, there are a few remedies that can help the situation dramatically. The first is barley straw.
Barley straw is a natural way of dealing of with pond string algae. It usually comes in netted bags, which can be placed directly into the pond. Over a period of time, microbes in the water will begin to decompose the straw. A byproduct of this process is the production of naturally occurring hydrogen peroxide, which helps fight both string algae and the algae that causes green pond water. When using barley straw, it's important to keep an eye on the ammonia levels in a pond since any decaying matter can potentially raise the amount of ammonia in the water. To learn more about ammonia and how biological filters convert ammonia into nitrate, please read our page on biological filters. The one downside of barley straw is that it takes a couple weeks to begin working.
Barley straw extract is similar to barley straw above, except the important part of the barley has been extracted into a liquid form making it faster and easier to apply to a pond. Because there is no need to wait for the straw to decompose for it to start working like with raw barley straw, the extract can begin working immediately after being added to the water. This is our preferred treatment for string algae here at Everything Ponds, and we recommend it for routine maintenance on a pond to promote water clarity. Another treatment we recommend for regular maintenance is a quality Biological Clarifier.
An electronic hair algae controller is a device that is usually fitted after the main filter system. As the water flows through a pipe, an electrical device generates pulses of random electricity, which effectively removes calcium from the water. Since calcium is essential to blanket weed, these devices can sometimes effectively kill off blanket weed over time. The reason we say 'sometimes' is that electronic algae controllers are very effective in some ponds, and in others, not as effective. There are varying theories as to why this is, the predominant belief being that as the string algae is broken down, essential minerals and salts are released into the water, which in turn helps promote growth of new algae.
Ultrasonic devices used to kill pond string algae are a relatively new technology to pond keepers. The idea is that the device transmits ultrasonic waves that are harmless to fish and other plants in a pond, but have a unique effect on algae. The ultrasonic waves work by destroying vacuoles in the cells that make up the string algae. The reason why other plants in the pond are not affected is because most other aquatic plants are multicellular, and not single cellular like most forms of algae.