Tech Bulletin: Do not use any products that add sulfates to your water!

In Blog, Maintenance Tips by David Jerkins

Certain products increase the level of sulfates/sulphates which is detrimental to all equipment, the pool surface, and the swimmer. They include, but are not limited to, products containing sulfuric acid, sodium bisulfate, thiosulfate, sulfite, or persulfates.

Salt Systems: Sulfates will cause a buildup of scale on the cell that produces chlorine, causing additional wear and tear and significantly shortening the lifespan of the cell. Many manufacturers are taking a hard stance against sulfates and voiding warranties for sulfate levels more than 200 ppm.

Pool Surfaces: Sulfates can become the dominant ion in the water, which can lead to a calcium sulfate scale. This scale is unlike the typical calcium deposits you may feel on the bottom of your feet in the pool. These crystals caused by sulfates can create sharp ridges that can cut the bottom of swimmer’s feet.

Concrete: Concrete is extremely durable and is known to last for a very long time. It is resistant to weather, abrasion, seawater, and most chemical attacks. Sulfates however, are one of its few weaknesses. So much so that concrete makers are constantly looking for ways to make their products more resistant to sulfates. The bottom line is that sulfates in pool water can damage concrete. Here’s a few papers done on the subject:

If you’d like to read further on sulfates and concrete, some papers on the subject:

Sulfate Attack on Blended Portland Cements

Sulfate-attack of Concrete

Metals: Sulfates have been found to cause corrosion of metals:

Report on the Corrosion of Certain Alloys

Effect of high sulfate concentration on the corrosivity: A case study from groundwater in Harran Plain, Turkey

What products to avoid?

  • Sulfuric Acid: An alternative to muriatic acid.
  • Sodium bisulfate: AKA “dry acid”. This can be in several forms, including tabs or granular.
  • Thiosulfate: Used to lower chlorine levels in the pool.
  • Potassium Monopersulfate: Used as a non-chlorine shock.
  • Sulfite: Another chemical used to quickly lower chlorine levels in the pool.
  • There may be others the writer of this blog is unaware of. Please read the labels on all chemicals to know what you are adding to the water. If the ingredient includes –sulfate or -sulfite it may be increasing the sulfates in the pool.

What should be done about it?

Test for sulfates in the pool water. If it is over 200 ppm, the only practical corrective action is to partially drain and refill the pool. Like cyanuric acid and others, the solution is dilution.

Think twice before using the products mentioned above. If you can avoid using them, do so.

If you would like a sulfate test kit, please reach out to