Reverse osmosis (RO/RODI)

The reverse osmosis system purifies mains water by removing chlorine, heavy metals, silicates and other substances. Produces basic water for each aquarium.

Detailed explanation

Tap water contains chlorine (or chloramine), copper from old pipes, silicates, phosphates, nitrates from agricultural pollution. All this ends up in the aquarium if you don't filter first.

Reverse osmosis forces water through a semipermeable membrane that blocks 95-99% of impurities. The result is almost pure water with TDS close to zero.

A RODI (Reverse Osmosis De-Ionization) system adds a deionizing resin after the membrane, bringing the TDS to practically zero. For marine aquariums the RODI is almost mandatory.

Maintenance of the system is essential. The sediment and carbon pre-filters must be changed every 3-6 months. The membrane lasts 2-3 years if the prefilters do their job. DI resin changes colour when exhausted.

Pay attention to the inlet water pressure. Below 3 bar the membrane works poorly and produces too much waste water. A booster pump solves the problem.

For freshwater aquariums, reverse osmosis is used to obtain soft water to be remineralised with specific salts (Salty Shrimp, Dennerle). For Amazonians and Caridines it is indispensable.

In ponds, reverse osmosis is rarely used due to huge volumes. It would be too slow and expensive. It is preferable to dechlorinate mains water with activated carbon.

Coralia Lab has a complete management system for the maintenance of the RO system: it warns you when to change the filters, monitors the output TDS, calculates operating costs.

How it is measured

The TDS (total dissolved solids) output is measured with a TDS metre. Under 10 ppm: membrane OK. Above 20 ppm: membrane to be replaced. After resin DI: must be 0.

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