Tap water is generally full of pollutants and the effect on your aquarium can be quite severe. RO Systems puts water through reverse osmosis leaving your water essentially free from chlorine, nitrates, phosphates and heavy metals. This water is an ideal base for making up salt solutions for your marine aquarium or for freshwater aquariums. We stock RO units for three different size aquariums. Aquariums which use 150, 75 and 50 gallons per day. We stock well known brands such as D&D.