Stop Algae Growth in its tracks! This natural pond treatment releases elements as it decomposes that prevents algae growth. Great against string algae, but also single-celled algae (pea soup algae). Barley Straw Liquid Extract is completely safe for your fish, frogs, snails, and plants.This is an algistatic additive as opposed to an algaecide, preventing algae growth but does not kill existing algae.