What do RO units do?
The primary function of a RO unit is to use a RO membrane to remove the "hardness" from the source water. This means that the RO membrane will remove primarily calcium and magnesium (which make up General Hardness, GH) and any carbonates (that make up the Carbonate Hardness, KH). This leaves us with truly soft water. Most RO units have a sediment and carbon pre-filter to remove large particulate wastes and organics and chlorine in the water. The Maxxima RO/DI also has a post-membrane chamber where the water is passed through a deionizing resin to remove some other chemical compounds often found in the water, primarily, nitrates, phosphates and silicates.
How does it work?
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 uses highly activated carbon to remove organics, pesticides, etc., from the water, in addition to neutralizing any chlorine in the water. This is especially important with TFC membranes, as the chlorine will degrade their performance. The RO membrane operates as a semi-permeable membrane that is placed under pressure (from the water supply) to cause water to pass through the membrane in a Reverse Osmosis direction, producing pure, soft water. As mentioned, the Maxxima series has a post-filter deionizing resin chamber to remove other small compounds that passed through the RO membrane with the water.
What else does it need?
The pre-filter cartridges and the deionizing resin will need to be replaced after 6 months or approximately 1000 gallons of RO water produced, depending on local water conditions. The RO membrane should be good for approximately 3 years.
What types of aquariums?
RO water makes a great source for water to be used to mix with your marine salt. RO water is also great for topping-off both marine and freshwater tanks to compensate for evaporation losses. For freshwater use, you need to add back electrolytes, as the RO water will be too pure for the fish or plants. You will also need to add some type of buffer, such as Superbuffer-dKH to prevent wild fluctuations in the pH value.