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.
Nearly every five and six stage under-sink reverse osmosis system sold in South Africa uses the same parts: three 10 by 2.5 inch cartridges in standard housings, an 1812 membrane in the long housing, and two inline cartridges after the tank. If yours is one of them, the cartridges here fit it whatever the brand on the housing. A tape measure settles it in a minute.
Measure the cartridge, not the brand
| The old cartridge measures | It is | Fits |
|---|---|---|
| About 25 cm long, 6.5 cm across | 10 inch standard | The three pre-filter housings of almost every under-sink RO |
| About 30 cm long, 4.5 cm across, with a short stem and two black O-rings at one end | 1812 membrane | The long membrane housing |
| About 25 cm long, 5 cm across, with a quarter-inch fitting at each end | Inline (T33 size) | The post-carbon and re-mineraliser positions after the tank |
| About 51 cm long, 11.5 cm across | 20 inch Big Blue | Whole-house units, not an under-sink system (its own guide) |
The three pre-filters
The first three housings take 10 inch cartridges with no end fittings: they simply drop in and the housing seals around them. The standard order is 5 micron sediment, granular carbon, carbon block. Some systems ship with two sediment stages or two blocks; the housings do not mind, so you can correct the order at the next change. The pre-filter kit is the three in one box.
The membrane
The long housing takes an 1812 membrane (some suppliers call the same size 2012). It is sold as 50, 75 or 100 GPD, which is how many US gallons it makes a day; all three fit the same housing, and the 100 GPD is the one to buy because it fills the tank fastest. Check the housing cap for a GPD figure if you want to match what was there; a higher figure never hurts.
The inline cartridges
After the tank sit one or two inline cartridges with quarter-inch push-fit ends: a post-carbon for the final taste, and on a six-stage system a re-mineraliser that puts calcium and magnesium back. Ours come with the fittings. The arrow on the body points the way the water flows, towards the tap. The 4-in-1 re-mineraliser replaces any single-stage mineral cartridge in the same position.
The few that do not fit
Some branded counter-top units and a handful of imported systems use sealed cartridges that twist into a manifold and carry the maker's own thread. They are not a standard and only the maker sells them. If the old cartridge has a moulded head with a bayonet or a screw thread instead of a plain open end, it is one of those. The cure is usually the system, not the cartridge: a standard housing set costs less than a year of proprietary refills.
The checklist before you order
- Pull one pre-filter and measure it. 25 by 6.5 cm is standard.
- Count the housings. Three short and one long is a five-stage system with one inline; add a second inline and it is six-stage.
- Note the carbon stages. If you have two blocks, order one GAC and one block and put the GAC second.
- Check the membrane housing cap for the GPD figure, or just take the 100.
- Order the full service kit for the year the membrane is due, the pre-filter kit for the six-month changes in between.
Questions
Will the AquaShield cartridges fit a system I bought elsewhere?
Almost certainly. The AquaShield uses the standard parts above, and so does nearly every under-sink RO sold in South Africa. Measure the old cartridge to be sure.
Does the brand of membrane matter?
The size matters; the brand less. A 1812 100 GPD thin-film membrane from a reputable maker rejects about 96 percent of dissolved solids. What matters more is changing the carbon block on time, which is what keeps chlorine off it.
My system has four short housings. What is the fourth?
Usually a second sediment or carbon stage, sometimes a mineral stage in a housing instead of inline. Measure it; if it is 10 inch standard, any of the cartridges here fit, and the order stays coarse to fine.
