A protein skimmer is a device that exports protein and other organic waste from water. For this reason, a protein skimmer is one of the most important pieces of filtration equipment for saltwater aquariums. Organic matter that is not removed from the aquarium will eventually break down into ammonia, nitrites and then nitrates. When a system's nutrient level is high, that waste becomes a major life-support system for difficult-to-eradicate nuisances such as hair algae and slime algae.