1 / 3RO Membrane, 1812, 75 or 100 GPD
Stage four. The one that does the purifying, in the two ratings systems were sold with.
A 1812 size thin-film composite membrane in the two ratings South African under-sink systems were sold with: 75 GPD (284 litres a day) and 100 GPD (378 litres a day), both rejecting about 96% of dissolved solids at 4 bar. The AquaShield ships with the 100; most other 5 and 6 stage systems with the 75, and the rating is printed on the membrane's label. Fits every standard 1812 housing. Changes every two to three years, or sooner if a TDS meter says so.
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- The cartridges our own plumbers fit on service calls
- Courier quoted at checkout, free on orders over R1 500
- Ships within 24 hours of payment
- 30-day returns on anything unused
How to tell it is time
Three signs. The tank takes far longer to fill than it used to. The water tastes of something again. Or, the honest way, a TDS meter: read the tap water and the purified water; when the purified reading climbs past a tenth of the tap reading, the membrane is letting salts through. A meter costs less than a membrane and takes the guessing out of it.
What shortens its life
Chlorine, above all. A thin-film membrane has no tolerance for it, which is why the carbon stages ahead of it must be changed every 6 months. After that, hard or high-TDS feed water (above 1 000 ppm) and low pressure, which makes the membrane work harder for less. On municipal water with the pre-filters kept fresh, two to three years is normal.
Fitting
Close the feed and the tank valve. Unscrew the membrane housing cap (the long horizontal housing on top of the bracket). Grip the old element by its stub with pliers and pull. Push the new one in, O-ring end first, until it seats. Cap on, valves open, and run the first two tanks to the drain, because a new membrane carries a food-grade preservative that tastes bitter.
Before you buy.
Read before you buy.
Which replacement cartridges fit my RO system? The 10 inch standard explained
Measure the cartridge, not the brand. Nearly every under-sink RO sold in South Africa takes the same 10 inch cartridges and the same membrane. How to check in a minute.
When to replace an RO membrane, and how to tell it is gone
Two to three years is the rule of thumb. A TDS meter and thirty seconds is the proof. Here is the test, the signs that come before it, and what shortens a membrane's life.
