A pool store tested my SWG, pool water, CYA level on 7/6/13: 73 ppm. After 3 - 5 inches of rain and three pump outs of excess water, I had the CYA level tested again on 7/27/13: 68 ppm.
I used Taylor test kit K-2005 and received a reading, repeated three times, of 45 ppm. Given an error factor of plus or minus 15 for levels up to 90 ppm, should I go with the store results or Taylor's?
Should I add, say, 10 ppm of CYA and test again and make comparisions with the store? If I get 55 and the store gets 78, which should I depend upon?
My real problem is, I do not want to put more CYA in the pool than necessary, and I do not want to go above 85 ppm of CYA.
Also, a side note: I recently read that no more than 40 ppm of CYA is necessary. Any truth to this?