Green pond, pond scum, pond moss are three commonly used terms to describe a grimy looking pond. Treating green scum can vary based on WHAT the scum really is.
There are a number of forms of algae that fall under these broad descriptions of scummy and green. Filamentous algae, also known as string algae, begins its life at the bottom of the pond, and then floats to the surface in large mats that can vary in color from bright green, dark green, to brown. Planktonic algae, also known as green water algae appears to turn the water pea soup green. This is because planktonic algae are very tiny suspended green particles.
Other common culprits often described as "pond scum" are duckweed and watermeal.These are some of the smallest aquatic plant species. Both duckweed and watermeal are prolific growers that float at the pond surface. Each tiny plant can produce a sister plant every 24 hours. This can quickly lead to complete pond coverage within weeks.
Treatments for all of the above described green pond issues use varying management techniques.
String algae- Kill existing algae mats with Cutrine Plus liquid algaecide. Spray directly on algae. For submerged algae growth, treat with Cutrine Granular. After treatment follow up with Pond Dye to limit regrowth.
Duckweed & watermeal- The most effective solution is to treat with Sonar A.S. or Sonar RTU because these treatments will spread throughout the entire water body to eliminate weeds. This treatment should only be used in ponds with very little to no outflow. For ponds with flow in and out, use Duckweed Destroyer Pack. This can be used to treat the entire pond or spot treat as growth begins.