100 GPD RO Membrane, 1812
Stage four. The one that does the purifying.
A 1812 size thin-film composite membrane rated 100 gallons (378 litres) a day, rejecting about 96% of dissolved solids at 4 bar. Fits the AquaShield membrane housing and every standard 1812 housing. Changes every two to three years, or sooner if a TDS meter says so.
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.
