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Yes, un-dissolved stabilizer (CYA) laying directly on pool plaster can easily cause a discoloration, especially with colored plaster.
Blue pigmented (colored) pool plaster is especially problematic, and can also be discolored (whitened) by other means and causes.
It can be bleached and made blotchy by simply maintaining the pool water with chlorine.
And all colored plasters can also become blotchy due to defective troweling and workmanship issues.
The location of the discolored area or areas, and pattern, may help in determining what caused the discoloration.
Yes, un-dissolved stabilizer (CYA) laying directly on pool plaster can easily cause a discoloration, especially with colored plaster.
Blue pigmented (colored) pool plaster is especially problematic, and can also be discolored (whitened) by other means and causes.
It can be bleached and made blotchy by simply maintaining the pool water with chlorine.
And all colored plasters can also become blotchy due to defective troweling and workmanship issues.
The location of the discolored area or areas, and pattern, may help in determining what caused the discoloration.