Wedneday night Cl measured 9ppm,
Thursday am still at 9ppm, with no sign of any deposits anywhere.

I'm thinking I'm either fighting pollen (as mentioned on other threads) or am on the brink of algae blooming below 8ppm.

I know this is not in line with POP, but I've hosting neighbourhood party coming on Sunday. Since whatever the deposits were are gone, and didn' seem to consume my Cl, I'm thinking I'll maintain Cl around 10ppm for the weekend, after Sunday let it drop to my 'normal' value around 5. If algae blooms I'll shock then.