Bleach Combining with CYA

[Jakebear]

How long does it take bleach (Chlorine) to combine (or whatever it does) with CYA and be "protected" from the UV. I drizzle it in around the side away from the skimmers.

When I add bleach in the evening --- 2 or 3 hours before sunset will it be effective or will the sun get most of it before the two get together??

I’ve read Ben’s tip which says after sunset but is it really that critical??

27000 gallon In ground Vinyl DE filter

[KurtV]

Bear,
I'm not sure that the CYA-Chlorine bind-time is all that critical here. Even assuming the best case, that the chlorine is protected immediately by the CYA, some part of the chlorine is still subject to destruction by the UV rays (that typical daytime chlorine losss that we all experience). My WAG is that up to 1 ppm of chlorine will be unecessarily destroyed by that 2-3 hours of sunbathing.

[medvampire]

One of the main reasons for evening treatment is economics. Why have the chlorine destroyed by the sun when by evening treatment it will have more time to do its stuff in the pool before the sun can kill it. I tried dosing in the morning due to I work nights. I found my chlorine useage drop by almost half in on very sunny days by doseing in the evening.
Steve

[chem geek]

As was said, the binding time of CYA and chlorine isn't relevant, but about 10% of the total chlorine binds with CYA per second so most of it is bound in a matter of seconds. More than 90% of the chlorine is bound in around 15 seconds (this is at a CYA level of around 30 ppm). So it's pretty darn fast and nothing to worry about. As was said, the reason for the nighttime chlorine dosing is so the higher levels of chlorine can be put to good use for disinfection and oxidation and then the next day somewhat less chlorine becomes the starting point for loss to sunlight (UV).

Richard