		Reverse Osmosis and Deionization of Water for Use in Reef Tanks	easy reefer > learning center
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Reverse Osmosis and Deionization of Water for Use in Reef Tanks

RO/DI Units

Reverse osmosis deionization units (RO/DI) are essential in the successful management of a reef tank. These units provide ultra pure water for a stable, predictable reef environment. The purified water allows the reef aquarist to determine and add only the essential trace elements and other essential nutrients to the water without any other unwanted metals or organic impurities.

So what is reverse osmosis deionization? In simple terms reverse osmosis is the process of water purification using a semi permeable membrane. The water is forced through a semi permeable membrane which has a known pore size large enough for water molecules to pass but does not allow metal salts, or other dissolved solids through. This process results in water that has had most of the total dissolved solids (TDS) removed. So the water is actually moving from an area of higher TDS concentration to an area of lower TDS concentration. This action is totally opposite of osmosis in which water flows from an area of low concentration to an area of higher concentration to reach equilibrium of the solution on both sides of the semi permeable membrane. That is why the process has been labeled reverse osmosis.

So why does the water go into a DI filter? The water goes through this extra process to remove any ions in the water. Ions are small enough to pass through the semi permeable membrane so the water must pass through a deionization filter which contains both cat ions and anions. These attracts either the positive or negatively charged ions depending on if they are cat ions or anions like magnets to further purify water leaving in theory only water molecules.

To make this process more efficient the water is passed through a sediment filter to remove any large complexes then onto a carbon filter to remove organic compounds, chlorine, and other simple compounds. These filters are necessary to extend the life of the RO and DI filters.

RO/DI units are expensive initially but they save the reef aquarist the hassle of purchasing purified water from grocery stores or their local fish store which is generally more expensive and sometimes questionable in terms of purity. RO/DI units are another useful piece of equipment in a successful reef tank.


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