Too much sunlight or excessive amounts of plant nutrients can cause algae to overtake a freshwater lake or pond. Nature supplies its own sanitation crew with algae-eating fish that thrive in a freshwater environment rich with nutrients. Take note of which kind of algae is overrunning your lake, as different types of fish are required to deal with different types of algae.
Siamese algae eaters are voracious when it comes to devouring red algae, also known as brush algae. Their peaceful temperament and appetite for red, brown and beard algae make them a good option to populate a lake or pond, though some have been known to become hostile towards their own kind as they mature. Few other algae-eating fish will consume red algae, but the common plec, or “pleco,” will sometimes eat it as well.
Brown algae, also called phaeophyta, includes giant kelp and many types of seaweed. Plecos, the most popular of the algae-eating fish, are known to eat brown algae, as well as red algae, blanched spinach and any driftwood available. However, those seeking to stock a lake with several algae-eating fish should take note that plecos can be quite aggressive, and will sometimes eat smaller fish.
Green algae is a favorite food of the otocinclus catfish. They enjoy eating soft algae after it has first formed, slurping it up with their suckermouths. Otocinclus catfish prefer to travel in schools of ideally six or more fish, and are less effective when separated from the school. The golden butterfly goodeid is another fish that will take on green algae, but should only be stocked in lakes with considerable space, as it is known to be violent towards other fish. The Siamese algae eater and the pleco are also green algae eaters.
Bright green beard algae resembles its name, and can be handled with butterfly goodeids, black mollies or Florida flag fish. Black mollies, also called balloon mollies, are friendly fish that specifically target fuzz algae, a less potent strand of beard algae. Unlike most other fish, they can survive solely on algae consumption if bred in an algae-rich environment. The Florida flag fish can also be an option, though it can be an aggressive fish and will eat shrimp and tetras as well as algae.