Quick Answer: On chlorinated or chloraminated city water, rebed with a 10% crosslink resin like ResinTech CNS10. It stands up to chlorine far better than standard resin. On a private well with no chlorine, standard Purolite C100E does the job for less. If your well has iron, choose a fine mesh resin like Provizio Supply's Carbochem fine mesh. Order the same number of cubic feet your tank held originally: 1 cu ft for a 32k unit, 1.5 for a 48k, 2 for a 64k.
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Before you spend money on resin, rule out the cheaper fixes. A lot of softeners that "stopped working" have a clogged injector, a stuck brine valve, a salt bridge, or a hardness setting that was never right in the first place. Resin is usually the last thing to go. When it really is worn out, you'll typically see a slow decline over months, not a sudden failure.
When it is the resin, the signs are pretty consistent:
- Hardness creeps back sooner after each regeneration, even with the settings unchanged
- Beads show up in faucet aerators or the drain line, which points to cracked, broken-down resin
- The resin looks swollen and mushy when you open the tank, a classic sign of chlorine damage
- The softener is 10–15+ years old on well water, or quite a bit younger on chlorinated city water
Our guide to resin life and replacement goes through these checks step by step. If you've ruled out everything else, here's what to buy.
In this guide
The one decision that matters: what's in your water
| Your water | Resin to buy | Why |
|---|---|---|
| City water with chlorine or chloramine | 10% crosslink | Chlorine attacks the resin's crosslinks. Higher crosslinking resists it longer |
| Private well, no chlorine, little iron | Standard (8%) | It's cheaper, and nothing in your water is attacking the beads |
| Well with dissolved iron | Fine mesh | Smaller beads have more surface area and tend to handle iron better |
| City water, very high flow demand | Standard or 10%, not fine mesh | Fine mesh causes more pressure drop |
Chlorine damage to resin is the main reason city-water softeners need new resin long before well-water units do. Chlorine slowly oxidizes the polymer backbone, and the beads swell and turn soft. With a 10% crosslink resin, that process takes much longer. If you're on city water, buy 10% and don't overthink it. Adding a carbon filter ahead of the softener also helps.
The five resins
ResinTech CNS10: the safe bet for city water
ResinTech is a major US ion-exchange resin maker. CNS10 is a strong acid cation resin built on a 10% crosslinked polystyrene matrix, and the listing pitches it specifically for systems with high chlorine, where standard resin breaks down. This one is sold by US Water Systems as a single 1 cu ft bag.
Buy it if: you're on municipal water and the old resin turned to mush in under ten years.
Downside: 10% crosslink resin is a bit denser and costs more than standard resin. On a chlorine-free well, you're paying for durability you don't need.
Purolite C100E: standard resin for well water
C100E is one of the most widely used softener resins. Purolite's spec sheet lists a total capacity of at least 41.5 kgr/ft³ in sodium form and a particle size range of 300–1200 µm. It's also certified by the WQA to NSF/ANSI-61 for drinking-water contact. This listing is a 1 cu ft bag sold under the Purolite brand. It doesn't come with a test kit, so grab hardness strips to confirm the rebed worked.
Purolite doesn't list a crosslink percentage on its product page. It's sold as the standard grade, not a 10% product, so don't use it on chlorinated water if you can avoid it.
Good fit for: private wells with no chlorine and little iron, where you want the most capacity for your money.
Provizio Supply Carbochem fine mesh: for iron
This is a 1 cu ft bag of fine mesh resin made by Carbochem and sold by Provizio Supply. The listing says it gives the same softening capability as conventional resin, with more exposed exchange sites for better ferrous iron removal. It doesn't publish a bead size, capacity figure or certification, so ask the seller if you need those. Smaller beads mean more surface area. That's why fine-mesh resin is the usual choice for softeners that also handle some dissolved iron, and why combination "iron pro" softeners ship with it.
Two caveats:
- Fine mesh is denser and causes more pressure drop, so it isn't a great idea for a big house with a tight flow budget on a small tank.
- It doesn't fix serious iron. Iron still fouls the resin over time, so pair it with an iron-fighting salt or a resin cleaner a few times a year. If the iron is above a few ppm, you need a dedicated iron filter.
Aldex C800x10: another 10% option
Aldex is a less familiar name, but C800x10 is sold as a 10% crosslinked softener resin and fills the same role as CNS10. It's worth comparing on price and stock when you need more than one bag, because 10% resin isn't always available in the quantity you want from a single brand.
We found less published technical detail for this product than for the ResinTech and Purolite resins. If NSF/ANSI-61 certification matters to you, and it should for drinking water, ask the seller for the certification before ordering.
10% crosslink refill kit with funnel: for your first rebed
If you've never rebedded a softener, this kit removes one annoying problem: getting resin into a narrow tank opening without spilling beads all over the floor. It's 1 cu ft of 10% crosslink resin (sold as the 32k size) packaged with a funnel.
What you give up: the listing doesn't name the resin manufacturer, so you're trusting the seller's 10% claim. If you want a named, certified resin, buy CNS10 and pick up a funnel separately.
Rebed, or just replace the softener?
A rebed is worth doing when the rest of the system is in good shape. Before you order resin, look at three things.
The control valve. A Fleck 5600SXT, Clack WS1 or Autotrol Logix that still programs and cycles normally is worth keeping. All three are long-lived, and seals, spacers and pistons are sold as parts. A proprietary cabinet unit with an obsolete circuit board isn't, because new resin won't save it.
The tank. Fiberglass-wrapped tanks last a long time. Look for weeping at the base, a bulge, or cracks around the threads at the top. If you see any of that, replace the tank, and at that point a complete new system often makes more sense.
The distributor and the gravel. If resin beads are getting into your plumbing, the distributor basket at the bottom of the riser tube may be cracked. A new distributor costs very little, and since the tank is already empty, now's the time to replace it.
Here's a rough way to decide. If the valve is good and the tank is sound, a rebed costs a fraction of a new softener and gives you most of the life back. If the valve is failing too, price out a complete system before you buy resin.
How much resin to order
Order the volume your tank was built for. Don't guess from the grain number printed on the box. Most sellers rate softeners at about 32,000 grains per cubic foot:
| Softener rating | Resin volume | Typical tank |
|---|---|---|
| 24k–32k | 0.75–1 cu ft | 8×44 or 9×48 |
| 40k–48k | 1.25–1.5 cu ft | 10×44 or 10×54 |
| 64k | 2 cu ft | 12×52 |
| 80k | 2.5 cu ft | 13×54 |
Check the tank label first, since the diameter and height are usually printed on it. Leave the original freeboard (the empty space above the resin bed). The resin bed expands during backwash and needs that space. If you overfill the tank, you'll lose resin down the drain on the first backwash.
How rebedding day usually goes
Shut off the water, put the softener in bypass, and depressurize it. Then unscrew the control valve, which is the hardest part on a tank that hasn't been opened in ten years. Siphon or scoop out the old resin. Leave the gravel underbed if your tank has one, and check the distributor tube for cracks. Cover the top of the riser tube while you pour so beads don't fall into it. Then pour in the new resin, fill the tank with water and let the resin hydrate before you reattach the valve. Run a full manual regeneration before you take it out of bypass.
There's a full walkthrough in our guide to loading resin into a mineral tank. Old resin can usually go out with household trash, but check your local rules. Our guide to disposing of old resin and components covers the exceptions.