Incoming mains water is pre-filtered with sediment and carbon cartridges before the RO membranes to produce water suitable for both marine and tropical fish. Marine fish have salts added back in to match conditions found where the fish originally come from. The main contaminates they are trying to remove are phosphates, nitrates and silica’s which all encourage the growth of algae. Chlorine and chloramines are removed to protect the RO membrane and also because they attack a mucus layer on the surface of the fish which otherwise encourages parasites to grow on the fish.
Bag filters are used for remove of general large contaminants including algae.
In addition aquatic shops supply RO water to the general public to top up fish tanks and supply carbon and sediment cartridges for filling garden ponds.