The HTH test kit and many other sources say the only way to lower the CYA is to drain some water.
My Pool is vinyl 5000 gal, soft water, Cal Hardness 150, DOES NOT LEAK, water 6 years old salt has gone from 3000 to 5400 ppm
Why do I have to put More Cyanuric acid in Every start up and During the year to keep it around 40.
By the way the pool is in great shape no problems with the water, just don't understand the lowering of the Cya.
Sparky
Found good answer here - - - >> http://www.poolforum.com/pf2/showthread.php/5762-Does-winter-(midwest)-impact-CYA-levels