Cation Resin Filter Cartridge

White crust on faucets. Spots on glasses. A kettle or coffee maker that scales up no matter how often you clean it. That is hard water: dissolved calcium and magnesium that come out of the water as scale wherever it is heated or left to dry.

The Crystal Quest Cation Resin Filter Cartridge is a water softening cartridge. It is filled with sodium-form cation exchange resin, the same type of resin that works inside a full-size water softener, packed into a drop-in cartridge for the places where scale does the most damage.

At a glance

• True softening: removes calcium and magnesium hardness instead of just conditioning it
• Less scale on faucets, glassware, kettles and other fixtures and appliances the treated water reaches
• Rated in grains: 805 to 5,200 grains of hardness capacity by size
• No tank, brine or drain line: it works in a standard filter housing
• Four sizes, 0.5 to 6 GPM, for countertop, under-sink and whole house housings

What you are looking at

A rigid polystyrene shell holds a bed of small cation resin beads, kept in place by a polypropylene expansion pad and followed by a spun polypropylene post-filter. End caps and a Buna-N top gasket seal it in the housing. Each bead is a cross-linked polystyrene sphere covered in sulfonic acid exchange sites, loaded with sodium and ready to trade it for hardness. Each end cap has 1-micron pads behind its openings.

How a water softening cartridge works

Ion exchange: sodium out, hardness in

Calcium and magnesium are positively charged ions (cations) with a double charge. The resin's sulfonic acid sites hold sodium, which carries a single charge. As water flows through, the resin pulls in calcium and magnesium and releases sodium in their place: two sodium ions for every calcium or magnesium ion it captures. Sodium does not form scale, so the treated water leaves no crust behind.

Why the resin prefers hardness

Strong acid cation resin holds double-charged ions much more tightly than single-charged ones. That preference is what makes softening work, and it is why the resin keeps capturing hardness until nearly all of its sodium has been traded away.

What grains mean

Water softening capacity is measured in grains of hardness. To estimate how many gallons a cartridge will soften, divide its grain rating by your water's hardness in grains per gallon. If your test reports hardness in ppm (mg/L), divide by 17.1 to convert it to grains per gallon. Harder water uses the cartridge faster; softer water stretches it.

Softening is not anti-scale conditioning

This cartridge removes hardness. A salt-free anti-scale cartridge, such as Eaglesorb ES3, leaves the minerals in the water and changes how they behave. Choose softening when you want the hardness gone; choose anti-scale when you want to keep the minerals and avoid adding sodium.

What it reduces

Primary target: hardness, meaning dissolved calcium and magnesium, and the scale deposits they leave behind.

Adds: a small amount of sodium, in exchange for the hardness it removes. Harder water means more sodium in the treated water.

Not designed to treat: bacteria and viruses, chlorine and chemical tastes, lead and other heavy metals, fluoride, nitrate or arsenic. Pair it with a carbon or SMART stage for filtration, and use it only on microbiologically safe water.

Is it right for my water?

A cartridge holds a small amount of resin, so it is best at softening the water for one point of use, such as a drinking water or appliance line, or for a cartridge system on moderately hard water. Test your hardness first and use the grain rating to see how long each size will last.

For softening a whole home, a tank softener holds far more resin. The Crystal Quest Whole House Water Softener carries 48,000 grains in its 1.5 cubic foot size. If you would rather keep the minerals and skip the sodium, look at Eaglesorb ES3 anti-scale.

Why Crystal Quest

• Real softening resin, the same sodium-form cation exchange chemistry used in full-size softeners.
• Grain ratings for every size, so you can work out how many gallons you will get at your hardness.
• Both paths to less scale: softening cartridges and tanks, and Eaglesorb ES3 salt-free anti-scale.
• Over 1,000,000 people served since 1994. Crystal Quest builds under ISO 9001 quality management, has made water filtration in the USA for over 30 years and offers lifetime support by phone, email or chat.

Where it fits

• Countertop and under-sink systems that take the 2-7/8" x 9-3/4" size.
• Whole house cartridge systems with slim 20" or Big Blue housings, on moderately hard water.

Choose the size printed on your current cartridge or in your order history: 2-7/8" x 9-3/4" (CQE-RC-04009), 2-7/8" x 20" (CQE-RC-04022), 4-5/8" x 9-3/4" (CQE-RC-04076) or 4-5/8" x 20" (CQE-RC-04071).

Common questions