String algae, also known as filamentous algae, shows up when water chemistry conditions in the pond favor algae growth. Ideal growing conditions for string algae include Nitrogen concentrations above 0.5 mg/L and Phosphorous concentrations above 0.1 mg/L.
String algae will grow under a variety of conditions, but it absolutely thrives in clear water with pH levels above 7.2 and Alkalinity (Calcium Carbonate) higher than 100 mg/L.
The most effective long-term treatments for algae include managing the nitrogen and phosphorous available in the pond or lake to essentially starve the algae. Because string algae initially grows attached to the bottom before detaching and floating to to the surface, pond dye to limit sunlight penetration can also be an effective treatment.
Nitrogen is removed from the water by beneficial bacteria (Pond Cleanse). Pond Cleanse bacteria work best in a high oxygen environment so aeration is recommended for best results. Phosphorus is a bit more challenging to remove and may require multiple treatments with a phosphorous binder (included in Bacteria Booster) or buffered Aluminum Sulfate.
For situations with continuous nutrient inflows, an aquatic algaecide treatment plan may be required to achieve control.
When using any effective treatment of string algae, the algae will detach from the bottom and float to the surface in mats when the treatment begins to work. This often results in the appearance that the algae bloom is getting worse. However, this is simply the dead and dying algae floating to the top. Keep treating and if desired, skim the surface algae to improve the appearance of the water body. To prevent floating mats, begin treatments early in the season so that algae growth on the bottom does not have an opportunity to begin.