When you head to the home-supply store to buy salt for your water softener, you are faced with a variety of products. One common choice is between coarse salt and salt pellets. The best one to use depends on your budget, the type of softener you have and how often you must regenerate the unit. The major difference between coarse salt and salt pellets is the level of non-salt impurities in the material.
Coarse salt is also known as "rock salt." It is a mined product, dug out from underground salt deposits. As a natural product, it is about 98.5 percent pure. The main impurity is calcium sulfate, which doesn't dissolve in water but instead falls to the bottom of the brine tank as sediment when the water softener goes through its regeneration cycles. Coarse rock salt is simply crushed and bagged for sale. Rock salt requires less processing than pellets, so it's normally less expensive. Coarse rock salt shouldn't be confused with solar salt crystals, a more expensive 99.5 percent pure product made by evaporating seawater with sunlight.
Salt pellets are made from mined salt that's been dissolved in water to form brine. The insoluble impurities drop to the bottom of the brine pan, and the pure brine is drawn off. The brine is heated to boiling in an evaporator, where all the water boils off. The salt left in the evaporator is 99.5 to 99.9 percent pure. There are only traces of insoluble impurities. The pure salt is removed from the evaporator, compressed into pellets and bagged for sale.
Why Impurities Matter
When you use coarse rock salt in your water softener, the impurities collect at the bottom of your brine tank and can eventually clog the brine tank outlet. The more often you regenerate your softener, the faster rock salt sediment builds up. To prevent softener malfunction when using rock salt exclusively, you should clean out the bottom of your brine tank about every four to six months. If you use only salt pellets, you won't have to clean your brine tank for years, even if you regenerate frequently.
Another difference is that coarse rock salt normally is sold without any additives, while pellet salt producers offer products with added compounds that help clean the softener and remove low levels of iron, under two parts per million, that may occur in the water. Different types of softeners work with different types of salt. The side-by-side units with separate brine tanks can work with rock salt or pellets because the brine tank is easy to access for cleaning. The all-in-one cabinet-style softeners are very hard to clean out, so they work better with pellet salt because it contains hardly any insoluble impurities to form sediment.