Local water supply is often clouded with many chemicals that may be harmful to the plant and animal life in your aquarium. With a reverse osmosis system, aquarium water is clear of harmful substances such as calcium, nitrates, phosphates, silicates, and water hardness. This will keep your aquarium life free of toxic chemicals. RO filtration allows you to maintain fish and reefs that are very sensitive and susceptible to these chemicals like freshwater fish and reefs in marine aquariums.