Mike the Poolman


Does High CYA Cause Pool Discolorations?

October 6, 2021

Reprinted with permission from Kim Skinner of OnBalance:

Several studies have shown that high cyanuric acid (stabilizer/conditioner) levels in pool water do not cause gray discoloration, white spotting (“spot etching” as some incorrectly call it) or staining of plaster swimming pools.

The Arch Chemical study in 2004-2005 provided evidence that high CYA levels (250 ppm) didn’t cause gray mottling discoloration or white spotting of pool plaster.

The NPC/NPIRC Cal Poly Phase 4 Pool Plaster study (2006-2007) showed that 250 ppm of cyanuric acid didn’t cause gray discolorations or white spotting, a different outcome than was anticipated. In fact, in comparison to pools with zero, 50 ppm, and 100 ppm of CYA, the plaster pools with 250 ppm CYA looked as good as the others.

A study by onBalance in 2010 placed plaster coupons into balanced water (0.0 LSI) with high CYA (150 ppm) and other plaster coupons into aggressive water (-0.8 LSI) with high CYA (300 ppm) for one year. The plaster coupons that were submerged in high CYA and balanced (0.0 LSI) water remained uniformly white and smooth (non-etched). The coupons that were submerged in high CYA and aggressive water resulted with minor and uniform etching of the surface, but still uniformly white. Neither of the plaster coupons resulted in any staining, gray mottling, or white spotting.

A more recent and comprehensive study, conducted by Kirk Mitchell and Associates, LLC., found that CYA levels of 250 ppm did not result in premature surface deterioration of plaster coupons. That report can be reviewed by going to http://www.poolhelp.com/wp-content/uploads/2019/03/JSPSI-Volume-6-Number-1-pp-24-32-Mitchell.pdf

Also, cement petrographers have identified the true causes of gray mottling (of white plaster) and spotting (of colored and white plaster) as improper troweling practices, along with adding excess calcium chloride and applying water during finishing. Those two plaster problems are not caused by high CYA, improper, or aggressive water chemistry as is sometimes incorrectly claimed.

For information on what really causes white spotting pool plaster, click: http://www.poolhelp.com/plaster-soft-spots/

For information on gray mottling discoloration click: http://www.poolhelp.com/home/onbalance-research/onbalance-research/how-white-pool-plaster-becomes-mottled-and-gray-discolored/

Unfortunately, so-called remedies for these two plaster defects, such as, performing acid treatments do NOT typically remove those discolorations, and instead, are detrimental to the plaster. Etching and roughness of the surface is often the result, which shortens the life of the plaster and increases the likelihood of future staining.

Note: If un-dissolved CYA (or trichlor tabs and granular) sits on a pool floor for any length of time, etching of the plaster may occur in those areas, since CYA and trichlor is acidic.

Reprinted with permission from Kim Skinner of OnBalance:

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