All Salt Is Not the Same
Generally speaking, staining, scale, and turbidity can often be attributed to the kind of salt used in the pool, as well as overall water balance. Salt can vary widely in levels and types of contaminants depending on where and how it was created. Salt is added to fresh water pools at levels of 3,000 to 4,000 parts per million, so a 20,000 gallon pool will require 530 pounds of salt at startup (to achieve 3,200 parts per million). With quantities that large, even salts that claim 99 percent purity can add up to 5.3 pounds of contaminants in the pool. These contaminants can slow dissolution rates and cause all kinds of maintenance problems, including staining, scale, and chlorine demand.
There are three kinds of salt that may be present in commodity pool salt:
Solar salt
Is created from the natural evaporation of saline ponds by wind and sun, may contain a host of organic contaminants that can cause turbidity and chlorine demand in the pool. Since an ECG has a fixed maximum rate of chlorine output, it can have a very difficult time overcoming the chlorine demand. Solar salt may also contain inorganic contaminants that cause staining and scale formation.
Rock salt
This is actually unrefined mined salt, may contain large amounts of inorganic contaminants such as manganese, copper, iron, nitrates, silicates, sulfates, calcium, and metals. Many of these contaminants can affect water clarity, dissolution rate, stain and scale potential, and other important water balance factors. Rock salt also contains dirt and other insoluble matter. For these reasons, it should never be used in swimming pools.
Mechanically evaporated salt
Often called “food grade” by the industry, this salt is created by the forced evaporation of saturated salt brines under controlled conditions. Mechanically evaporated salt is best for saltwater pools because it is purer than rock salt and solar salt. But don’t let the terminology confuse you. You would never add food salt to a pool; it usually contains iodine and anti-caking agents, such as YPS, that can cause issues in swimming pools.
Not all mechanically evaporated salt is equal, as some forms contain higher levels of contaminants than others. Where your salt was created is equally important as how it was created. Interestingly, Canada has some excellent mines that produce very high-quality salt. Mechanically evaporated salt from Compass Minerals’ Sifto facility in Amherst, Nova N.S., with all other leading North American salt producers. (This salt is used in a new saltwater pool product called Pristiva™, which is available in the United States and should be available in Canada within the next few years.)
It can be difficult to determine what kind of salt is in commodity pool salt. Some brands use salt from many different sources, which can vary from region to region. Most brands use salt from whichever mine is closest to their final ship destination to minimize shipping costs. Pristiva is the only brand that guarantees that its salt comes from the same source in every bag.
