What chlorine level to shock -- now that half my CYA is gone

[JimK]

I've pretty much given up explaining everything I see happen in pools. Sometimes, years later, I find out what was going on, but mostly not. Weird stuff happens from time to time in pools, and unless your goal in life is to be an amateur chemical detective, it's better to let it go UNLESS it's causing a real problem. Who knows, if you have a dog, maybe this:

is the explanation.

If you are regularly adding Jacks Magic, you may want to get and use some CuLator packs. They are not effective for quick clean-up, but they do continuously remove metals from the water, unlike products like Jacks Magic which work temporarily to keep it soluble. If you do get some, do NOT throw them away monthly, like the company encourages. They are not 'used up' till badly discolored OR fouled with goop. Keep one in your skimmer, but use a skimmer sock on top to protect the pack from 'goo'. You can also just chuck them in the pool. The more you have, the more effective they'll be. Just don't put them where they will get ruined with greasy dirt. (So, don't put them in a chlorine floater, where lotion and suntan oil can foul them.)

1 ppm Culator
1.5 ppm Culator, sold by Amazon
4 ppm Culator, sold by Amazon
Poolmaster 16242 Poolmaster Skimmer Basket Liner

Thanks Ben. There's no sign of algae or anything, so as you suggest I'll just write it off as a quirk and move on.

LOL.....no dog here. 99.99% of the time it's just the two of us using the pool.

Once I get CL levels stabilized and the SWCG set, I'll look at addressing the metal issue. BTW, last year you had me do the bucket test for metals. Despite the results being negative for metals, the stairs starting staining again when I stopped adding sequest (6 oz a week after the initial does of 2 qts does the trick).

My hesitation with the Culator is cost. At least if used as recommended, it costs more to use the Culator than the sequest, not to mention that for some time I'd have to use the sequest and the Culator together, increasing cost further. Then add the cost of the skimmer socks, which would likely get clogged quickly and require frequent replacement due to all the nearby trees. So it seems that going with the Culator would cost more and add more maintenance than just adding the sequest once a week. I would like to persue this discussion further, but I'll start another thread for that at a later date when I'm ready to tackle it.

I bet it was the polyquat that caused the drop in FC.

Now that you mention it, I do think I remember reading that polyquat increases CL demand? If so, I think that may be it. Thanks for pointing that out.