Green hair algae (GHA) is a common annoyance for owners of both freshwater and saltwater aquatic systems. This filamentous algae, often belonging to the genus Oedogonium, grows in long, stringy strands that quickly cover decorations, substrate, and plants. GHA indicates an imbalance in the aquatic environment, specifically related to nutrient levels and light. While GHA is not toxic, its rapid growth can obstruct views. Managing this growth involves introducing natural herbivores, a method known as biological control.
Biological Control in Freshwater Environments
The most reliable biological tool for managing GHA in freshwater aquariums is the Amano shrimp (Caridina multidentata). These shrimp are renowned for their voracious appetite for various algae, including the tough, filamentous strands of GHA. They are tireless foragers, constantly picking at surfaces and detritus, making them highly effective in large numbers. Amano shrimp prefer to eat GHA when other, softer food sources are not readily available.
Siamese Algae Eaters (SAE, Crossocheilus oblongus) are highly valued for their willingness to consume GHA, a trait few other fish share. SAEs can grow up to six inches, requiring a tank of at least 30 gallons, and they remain diligent algae eaters even as adults. It is important to correctly identify the true SAE, as look-alikes like the Flying Fox often lose their algae-eating habits once they mature. The black stripe on a true SAE extends fully into the caudal (tail) fin, distinguishing it from other similar species.
Nerite snails (Neritina species) contribute to the cleanup crew by targeting shorter, softer algae, though they will graze on the base of GHA growth. These snails are helpful because they will not overpopulate the tank, as their eggs require brackish water to hatch. While they may not consume long strands of GHA, their continuous grazing on surfaces helps prevent new patches from taking hold.
Biological Control in Saltwater Environments
Marine aquarists rely on a dedicated cleanup crew to keep nuisance algae like GHA in check. The Emerald Crab (Mithraculus sculptus) is known to eat GHA, using its claws to pull apart and consume the strands. These crabs are effective against both GHA and bubble algae, a common saltwater pest. However, if the crabs run out of algae, they may begin to pick at corals or smaller snails, so their diet must be monitored.
Various species of snails form the backbone of the saltwater cleanup crew, with Turbo snails and Trochus snails being particularly effective against GHA. Mexican Turbo snails are large and consume substantial amounts of algae, but they may inadvertently knock over loose decorations. Trochus snails are smaller, more adept at navigating rockwork, and capable of self-reproduction in a reef tank environment. Both types of snails are most effective at grazing on shorter growth, meaning longer strands of GHA may require manual removal first.
Certain fish specialize in GHA removal, though they are usually reserved for larger systems. Herbivorous fish like the Lawnmower Blenny (Salarias fasciatus) or Tangs (Zebrasoma species) graze constantly on algae-covered surfaces. Blennies are suitable for tanks over 30 gallons, while Tangs require much larger tanks, often 75 to 100 gallons or more. Sea Hares, a type of marine slug, are extremely effective, capable of clearing massive outbreaks quickly. However, they require a constant supply of algae and must be relocated once the GHA is gone to prevent starvation.
Addressing the Underlying Cause of Algae Growth
Introducing herbivores provides a temporary solution, but persistent GHA indicates a fundamental imbalance in the tank’s chemistry. Algae growth is primarily fueled by excess nutrients, specifically nitrates and phosphates, which accumulate from fish waste and uneaten food. Water testing often shows low nutrient levels during a severe outbreak because the algae is rapidly consuming all available nutrients. Excessive light, particularly high intensity or long duration, is the other major driver. Reducing the photoperiod to eight hours or less can immediately slow GHA growth.
Controlling the nutrient source requires consistent maintenance practices, such as performing regular water changes and avoiding overfeeding. Non-biological tools like Granular Ferric Oxide (GFO) or biopellets can be used in saltwater systems to chemically bind and remove phosphates and nitrates. Manual removal of large GHA patches is also necessary, as this physically exports the bound-up nutrients from the aquarium.