I wanted to share another reason why a water softener stops using salt.   Salt is sold in Pellets or Crystals.   Over time pellets sitting in the bottom of the brine tank can start to turn into mush instead of dissolving.   As you add salt the weight compresses the mush and turns into a solid block.   That block will not dissolve, causing the water level in the brine tank to rise.   In time the water will get so high that it engages the safety float.   The end result?  The water softener will use less salt, eventually no salt.  It will keep regenerating but the resin bed will not be recharged sufficiently and will no longer produce soft water. 

That is why we recommend the use of Solar Salt.   The crystals do not break down into a mush like pellet salt and thus eliminates the problem all together.