CC defying pool physics?

[EricH]

Yeah, chem_geek tried to help me with the CYA over on this thread:
http://www.poolforum.com/pf2/showthread.php?t=7705

Unfortunately, my Taylor reagent never shows enough reaction with my water to block the dot from view - so my assumption is no CYA.

To the point of your answer, though: is it that CYA will inhibit the ability of free chlorine to "neutralize" combined chlorine? So at the very least, I could try driving my shock level up to 25 or more to see if that helps (and maybe tell me what my true CYA is despite the Taylor test!)

Thanks,
E

[chem geek]

You are correct that the rate of Free Chlorine reaction to break Combined Chlorine will be slowed down by more CYA since it is the disinfecting chlorine (hypochlorous acid) that does the actual breakpoint. Ironically, the formation of new Combined Chlorine also comes from the disinfecting chlorine so exactly what happens depends on the types of substances that are in the water since disinfecting chlorine combines with ammonia very, very quickly, but breaks monochloramine (chlorine combined with ammonia) more slowly. Other organics may have the opposite behavior.

In any event, it is sunlight that helps break down combined chlorine at reasonable rates, along with the chlorine of course. So if you keep your pool covered or if it is not exposed to sun, then you may find more CCs that are hard to get rid of. It is also possible to have "persistent combined chlorine" that doesn't go away, but again this is more typical in indoor pools with no sunlight.

I'm not sure why your Taylor CYA test doesn't have the black dot disappear. If it gets cloudy at all, then there is CYA in the water. This link to the Taylor website shows how the black dot goes from being visible, to clouded, to obscured as you add more sample to the tube.

Richard