Mike the Poolman


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High Cyanuric Acid (CYA) issues with plaster

January 9, 2014

Reprinted with permission from Kim Skinner of On Balance:

Contrary to some misinformation that has lately been floating around, high cyanuric acid (stabilizer) levels do not cause gray discoloration, or white spotting (“spot etching” as some incorrectly call it) in plaster swimming pools, no matter what.  And there are several studies that have documented that.

The NPC/NPIRC Cal Poly Phase 4 study (2006-2007) showed that 250 ppm of cyanuric acid (CyA) didn’t cause gray discolorations or white spotting. In fact, in comparison to pools with zero, 50 ppm, and 100 ppm of CyA, the plaster pools with 250 ppm CyA looked the best overall after ten months.

A study by onBalance included placing a quality plaster coupon into (balanced LSI) water with 150 ppm of CyA, and an identical coupon into aggressive water (low TA) with 300 ppm of CyA. They were left there for one year. The picture below shows that the coupon submerged in 150 ppm CyA remained uniformly white and smooth (non-etched), and although it is hard to see, the coupon submerged in 300 ppm CyA had slight uniform etching and some exposed aggregate showing at surface. Note that neither of the plaster coupons resulted in gray mottling or white spotting.

The Dow Whitney study (University of Florida, 1990) concluded that Cyanuric acid alone did not appear to be a cause of leaching even at 500 ppm!

The 2004-2005 Arch Study provided further evidence that high CyA levels don’t cause gray discoloring or white spotting of pool plaster. Their study did show uniform etching (degradation) of the plaster coupons due to the water being aggressive, but not from high CyA only. It appears that the alkalinity had remained on the low side and was not adjusted upward to balance the water (per the LSI) when higher CyA levels (250 ppm) were maintained.

Why write about this high CyA issue?  Because there is one pool plasterer (and NPC member) that teaches at pool trade shows and at service tech’s chapter meetings that high CyA levels (above 50 ppm) causes gray discoloration and white spotting (spot etching). What studies does he cite as supporting his opinion? The same NPC/NPIRC and Arch studies mentioned above, which in reality, don’t support his claim at all, and in fact prove just the opposite. 

On Balance, January 2014


Mike the Poolman
Pool Service & Repair in Folsom, CA since 1995


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