CYA "poll"

[waterbear]

I think one of the "chemistry buffs" can explain this more technically that I can, but my understanding is that the CYA doesn't "tie-up" the free chlorine - if it did then it would change to combined chlorine (which is bad).

The cya DOES tie up some of the FC and covert it to a class of 'combined chlorine' called chloramides which are stronger oxidizers and sanitizers than chloramines but not as strong as hypochlorous acid (FC). In the past sometimes anhydrous ammonia was used to help stabilize chlorine in pools by forming monochloramine, which is an effective sanitizer (Some mustard algae treatments today still depend on this chemisty).
www.usace.army.mil/publications/armytm/tm5-662/chap6.pdf has some interesting info on stabilization of chlorine.
(Chloramides are just a type of combined chlorine that will still test as FC with a test kit and still has some sanitizing ability but at a lower rate.) However, this form of combined chlorine is resistant to UV. At least this is how I understand it. Cyanuric acid is an ammonia/nitorgen compound with a ring structure .It is in a group of chemicals called triazines. (Does anyone recognize that from the full chemical name of trichlor or dichlor?) I am trying to find more info on the chemisty of this right now and can only find bits and pieces here and there.