I know the CYA "black dot" test can vary greatly between users based upon light, experience, etc. Yesterday was cloudy and I wanted to some chlorine into the pool as I had opened it up two days earlier. I had read the CYA to be about 60. Basing everything on pool school, my schock value should have been 24, and maintance level 7. That called for 11 gallons of 8% bleach. I added 10 because I thought I might be a little off with the CYA. Last night my free chloroine was 28 and thats where it is today. I reran the CYA today in the bright sunshine and came up witha 45. That would put my true shock vaule closer to 19 - 20. So one observation and one question.
1. All CYA tests are terrible...anything that is that technigue depenend cant be reliable on a daily basis.
2. My current shock value is about 10 ppm then it should be...will that harm the liner?
Also, if I ever take my water to Leslies for them to do the CYA test (last year I was out of reagent), they are always way lower then what I get...at least 20 - 30 PPM. My belief that the popularity of SWG is due to the fact that people take use stabilized pucks in feeders, take their water to places like Leslies, who under read the CYA level, the current amount of free chlorine they have isnt high enough to work effectively and half way through the year they get algae....they switch to e SWG and dont have any issues becaus ethe SWG keeps adjusting the amount of free chloroine and does not add CYA to the water....thus all is good....just my 2 cents. Also my leslies never tests for free chlorine, just total...another issue.
So if anyone can just let me know if I shold be wooried abot my shock value I would appreciatte it.