That Fish Blog – Aquarium Advice and Information

Hi everyone, Justin here. Working on the sales floor, we get a lot of technical aquarium questions, many involving water quality.  Today, I’d like to talk a little about reverse osmosis and what RO units do.  RO, or Reverse Osmosis units are the best way to ensure that your water is perfectly clean. Reverse osmosis is a process in which dissolved solids are removed from water. The pressure from your tap forces the water through a semi permeable membrane that allows only water to pass through. The contaminants are then washed out in the waste water.

There are many factors that will determine the efficiency of your RO filter. Incoming water pressure should be around 60 psi. This is standard pressure coming from most hoses and sink faucets. If the pressure is too low, a booster pump may be necessary to increase the pressure into the RO unit. Water temperature is another important factor. Water that is too cold will cause a drop in pressure, while water that is too hot will damage the membrane. A suitable temperature range is 60-75 degrees F. Total dissolved solids, or TDS, is the measure of the amount of solids dissolved into your water. The higher the TDS in the tap, the quicker the membrane will wear out and need to be replaced. The age and quality of the membrane will also determine the effectiveness of the RO. A new membrane will pull out more TDS than an older membrane. A higher quality membrane will also be more efficient and last longer.

RO membranes will remove contaminants on an ionic level. This means that the membranes will remove single ions and particles as small as 0.001 microns. As a reference, the smallest known bacteria is approxiamately 0.200 microns. Below is list of the ions removed and an average percentage removed:

TYPICAL REJECTION CHARACTERISTICS OF R.O. MEMBRANES Elements and the Percent R.O. Membranes will remove
	Sodium Sulfate Calcium Potassium Nitrate Iron Zinc Mercury Selenium Phosphate Lead Arsenic Magnesium Nickel Fluoride Manganese Cadmium Barium Cyanide Chloride	85 – 94% 96 – 98% 94 – 98% 85 – 95% 60 –75% 94 – 98% 95 – 98% 95 – 98% 94 – 96% 96 – 98% 95 – 98% 92 – 96% 94 – 98% 96 – 98% 85 – 92% 94 – 98% 95 – 98% 95 – 98% 84 – 92% 85 – 92%
% may vary based on membrane type water pressure, temperature & TDS

There are two different types of membranes commonly available, CTA and TFC. CTA stands for cellulose tri-acetate and is safe for use with chlorine-based water sources. CTA membranes should be used for City Water sources. TFC stands for thin film composite and is not safe for use with chlorine based water sources. TFC membranes must be used with well water, or chlorine free water sources only.

Inside the lines of each RO unit are flow restrictors to ensure proper pressure and flow over the membrane. These flow restrictors are small “dams” or nozzles that allow only a certain amount of water flow through the lines. The membranes coupled with these flow restrictors are made to handle the maximum flow of water through the restrictors. Placing a membrane rated too low into the unit will ruin the membrane, while placing a membrane rated too high will not increase production of water.

There are many different styles of RO filters available. 2 Stage and 3 stage filters are the most commonly available, but other higher stage filters are also available. On all two stage RO filters, there is the membrane, a micron cartridge, and a carbon block. The micron cartridge pulls out tiny particles that may be in the water. The carbon block will pull out any organic contaminents before entering the membrane. The membrane is the last stage in all 2 stage filters. In 3 stage filters, the last stage is a deionization cartridge. The deionization cartridge or DI removes any ions that may have passed through the membrane. The 3 stage RO/DI filters are the most efficient and will guarantee clean water.

I hope this article helps you to understand what RO units do and how they benefit your aquarium and the fish you keep.  Feel free to comment or ask any questions you may have!

Thanks,

Justin