Understanding your Reverse Osmosis unit

Understanding your Reverse Osmosis unit


The water you add to your reef tank is the most important factor for any type of success. Municipal, well, and "tap" water sources often contain copper, manganese, lead, nitrate, phosphate, disinfection chemicals and other substances that make will do harm to a reef aquarium full of fish, corals and other invertebrates. The best defense against these contaminants is a reverse osmosis filtration system or RODI. Reef enthusiasts rely on their RO system to ensure the saltwater they mix up is consistently safe for their tanks, containing zero total dissolved solids. The same goes for top-off water. Your reverse osmosis system needs periodic maintenance to keep it working properly. If not, it will allow contaminated water through the system, causing water quality problems in the short and long term. Here’s everything you need to know to maintain your RO or RO/DI system.


Sediment Pre Filter

The sediment pre-filter cartridge is designed to protect the filtration system from clogging or damage caused by fine particles such as iron oxide, sand, and mineral scale. Over time, these small particulates can clog the tiny flow restrictors and activated carbon filters. The pre-filter is made of spun polyester fibers designed to capture these fine particles. As the fibers clog with sediment they also become coated with naturally-occurring bacteria slime. Clogged pre-filters will reduce flow to the rest of the reverse osmosis system eventually. How to tell when to change the RO or RO/DI pre-filters is if the pressure gauge readings decline, otherwise, we recommend these be replaced every six months to maintain maximum water production.


Activated Carbon Cartridge

The activated carbon cartridge follows the prefilter. Your RO may use a granular carbon or a solid carbon block cartridge. The role of the activated carbon cartridge is to remove chlorine and chloramine disinfectants. Activated carbon also removes organic compounds such as pesticides, carcinogenic disinfection by-products and naturally-occurring organics.  Carbon cartridges should be changed about every six months when maintaining your RO or RO/DI system. Just like the prefilter, activated carbon will eventually become coated with slime and stop removing chlorine and chloramine.

Reverse Osmosis Membrane

The heart of the RO system is the reverse osmosis membrane also called the TFC membrane. A semi-permeable membrane is wound around the center core. As water is forced through the membrane, minerals, nitrate, phosphate and metals are stripped from the water and sent to the wastewater line.  The membrane works by “rejecting” the contaminants from the water stream. But they must be flushed away to keep the membrane working.  Over time all RO membranes become fouled with calcium carbonate, bacteria and other contaminants.  How to maintain and extend the life of the membrane is with an RO Flush Kit.  The flush kit loosens and washes away minerals and contaminants that clog the membrane.  The easiest way to monitor the status of the RO membrane is with a TDS meter. Whether hand-held or in-line, the meter will show when minerals and salts begin slipping past the membrane. This signals that the RO membrane needs to be replaced.


Deionization Cartridge

Reverse osmosis alone does not produce extra-pure water. RO removes a percentage of the contaminants. Certain substance like nitrate and silicate are hard for the RO to remove. That’s why a deionization cartridge(DI) is often the last stage in the water purification system. DI uses ion-exchange resins to scavenge out any trace of silicates, phosphate other undesirable substances. Once the resin is used up, it stops working. DI resin cartridges will cause the water to have a “fishy” odor when used too long. If your DI cartridge use color-changing resin to indicate when it needs to be changed, change it as soon as the cartridge changes color. You can also use a hand-held TDS meter to monitor the quality of your water after the DI cartridge.