A water softener works in two stages. Each regeneration draws brine from the salt in the brine tank, and that brine flushes the resin bed clean. When the salt stops dissolving, the controller can still run its cycle on schedule, and the house can still get hard water. The most common cause is a salt bridge, a hard crust that forms over the water and leaves an empty gap underneath. The salt above looks solid, so nothing seems wrong until spots and scale begin to show up again.

What a bridge looks like and why it forms

Salt sits on top of the water in the brine tank. As it dissolves, the surface can harden into a layer that bonds together, and humid rooms, the type of salt you buy, and how much salt you load at once all affect how quickly that happens. Once the lid is in place, water cannot reach the salt below it, and the tank holds a pocket of air where brine should be. Salt mush, a soft sludge at the bottom of the tank, is a related problem. It usually comes from impurities in the salt or from too much water sitting in the tank, and it can block the brine valve or cover the salt you need.

The signs that show up before a test does

Check the brine level between regenerations, not only when you refill. If you have looked after several cycles and the level has not dropped, the salt is not dissolving. A bridge can also hide itself: the water may look high enough while the salt above it stays put. Other early signs include soap that lathers poorly, glass and shower doors that spot again soon after cleaning, and kettles, faucets or aerators that build scale faster than they used to.

Test the water at a tap after a regeneration with a home hardness test kit or strips. Compare the result with a reading you took when the unit was working well. A reading that drifts upward means the softener is not making soft water, even though the controller reports a normal cycle. Write the reading down so you can see the trend rather than relying on memory.

What to check, in order

Follow your owner's manual for the exact steps, and keep the unit powered on so you can see how it responds. Open the lid and look into the brine well with a flashlight. Note whether the salt is level, whether there is a hard crust with air beneath it, and whether there is sludge on the bottom. Keep a short note on the tank or in your maintenance log with the brine level and whether you saw a crust, and add a line each time you look.

If the manual allows it, break a crust with a blunt wooden or plastic handle, not a metal tool that can scratch the tank or damage the valve area. Break it only as far as needed to let water reach the salt below. Remove any sludge the manual says to remove, refill with the salt type the manual specifies to the level it recommends, and run a manual regeneration. Then test the water at a tap again. If you are not comfortable opening the brine well or breaking a crust, ask the service provider to do it and to show you what they found.

What to ask before you pay for service

When you call for service, ask what they found in the brine tank and whether the fix was cleaning, salt replacement, or repair of a valve or float. Ask whether the salt they recommend is rated for water softeners, whether the visit includes cleaning the brine tank, and whether they will test the water at a tap before they leave and after the repair. Compare quotes on those items, not only on the visit fee. A quote that skips the tank cleaning or the water test may leave you with the same problem in a few weeks.

When to stop and call

If you break the crust, clean the tank, refill, run a regeneration, and the tap reading is still high, the salt alone is probably not the whole story. The same is true if the brine level drops but the water stays hard, or if the unit makes unusual noises or leaves water in the brine well after a cycle. At that point, stop adding salt and have a qualified service provider inspect the valve, the float, and the resin bed. Keep your readings and notes with you when you call, since they show the pattern better than a single test does.