AQUARIUM RO SYSTEM INFO
All aquariums should use RO water because tap water contains many impurities. These impurities include phosphate and nitrates, which fuel algae growth. Copper--highly toxic to invertebrates--can be leached from household pipes.
What do RO and RO/DI units do?
The TFC membrane removes calcium and magnesium (which make up general hardness, GH) and any carbonates (that make up the carbonate hardness, KH). This leaves you with truly soft water.
The Sediment pre-filter is a fine (1 or 5 micron) mechanical filter to trap large particles in the water, and some bacteria.
The Carbon pre-filter removes large particulate waste and chlorine in the water. This is especially important with TFC membranes, as the chlorine will degrade their performance.
The Deionization (DI) cartridge found in RO/DI units removes some other chemical compounds often found in the water--primarily nitrates, phosphates and silicates.