What is R.O. water?
Reverse osmosis, or R.O. water for short, is water that has been stripped of it's mineral content by a membrane that only allows pure water molecules to pass through it's matrix. The result is purified water that has very low hardness and pollutant levels and can be used for keeping demanding fish or marine invertebrates such as Discus or Corals. Although R.O. water is ideal for expert aquarists keeping delicate species, it is equally suitable for the average community tank - especially in areas where tap water contains high levels of nitrate or phosphate.
As R.O. water is so low in essential minerals, it is normally necessary to add buffering products to prevent problems with pH. Different buffers are available for freshwater or marine use and should be added before using the water in your aquarium.