Saltwater swimming pool

These days, salt stains in swimming pools are very common.  This is because salt is sourced from many places in Australia and around the world. This means that the quality of salt that you purchase can vary dramatically from batch to batch. This means that one bag can be great and the next bag could be very badly contaminated. These huge quality variations have led to an increase in salt stains in Australia.

Good pool salt

  • Good salt dissolves fast
  • Good salt is bright white
  • Good salt has small cystals
  • Purity is greater than 99.5%

Bad pool salt

  • Salt takes ages to dissolve
  • Water turns brown after adding
  • Salt was really cheap
  • Salt stains the pool floor
  • Crystals are large
swimming pool salt

Large quantities of salt are harvested using pretty basic methods.  As the picture shows the variation in colour and quality of salt can vary depending on where in the pile your salt is collected.

Pool salt staining is on the rise

Since the rise of big hardware stores in Australia we have seen the quality of salt decline. These companies negotiate massive volume deals with suppliers at low prices. So, because of their huge buying power they are able to sell it cheap. However, the market price of salt varies according to the quality of the salt. For more about this please see our blog post about pool salt. Remember, in most cases, cheap salt is cheap for a reason.  Cheap salt has more mineral, water and other impurities in the batch.  Remember, the grade (or quality) of salt determines the market price.  

Mineral pool salt

Some pool owners will decide to add magnesium salts to their pool to gain the benefits of mineral salts. However, if your water is not properly prepared then this plan can backfire badly as the pictures show. Magnesium salt is rich in magnesium chloride which can stain pools if the water is out of balance. Remember, if you are planning to convert your pool to a magnesium system then make sure that you balance the water properly before you add the salt and make sure your chlorinator is compatible with magnesium salts.

Salt in swimming pool

How salt stains happen

Salt is a natural product that comes from the earth. Because of this, it means that minerals, metals and other contaminates can be absorbed into the salt crystals. What’s more, when the salt is added to the water these contaminates are released into the pool water. As a result, some people say that the moment they  added the bad salt to the pool, the water turned brown or dark green almost right away. This happens because the minerals and metals in the salt are now floating in the water. Once these minerals and metals are in the water for long enough they will start to stain the surface of the pool. The picture below shows how heavy copper staining can impact a pool surface. This person regularly left the salt to dissolve on the steps of his pool. Salt stains can be removed from swimming pools without draining but it is best to avoid them in the first place.

For years this pool owner poured salt bags on the steps and shallow end of the pool.  Over time the staining on the surface became so imbedded into the surface of the pool that it turned black.

copper staining in pool