I understand the relationship of Chlorine and Cya level in that you increase the chlorine from when you start out at zero to like what I have now which is 30ppm cya. I found a comment which sort of was what I was thinking in that although your tester indicates 3ppm in your pool it is not a true reading cos of the amount of CYA in the pool. Its like its being available chlorine but its not Free chlorine.
If this is true ,is that why it dosent irritate your eyes at 3ppm at 30ppm CYA and at 0ppm of CYA it WOULD be more irritating at 3ppm of chlorine. either way it still registers on the pool pentair and strip testers the same. So it seems to me that if it registers it must be there but in a more inefficient way ie. dosent kills germs as well and dosent irritate the eyes as much.
Also if this is rubbish then why dont we just put in 3 ppm of chlorine and stick to that level until the cya is way up to 50ppm and stop having to check the chlorine from 1ppm upwards