Too much work had me busy last week, and I went 3 days without testing or feeding chlorine. I can usually go 2 days without issue, this time FC level fell too low, to 2 ppm. I came home to find yellowish patches on the wall on the north facing, shaded side, which brushed off for the most part so I assumed mustard algae. Raised FC to shock level (24 ppm @ 55 CYA), cleaned cart filter and ran filter 24/7 the last 2 days. What I'm finding now is that the patches are not brushing completely off, and in that affected area some small pieces of diamond brite seem to be eroding off, something I've never seen before. I've owned the house 2 months, this is new to me, don't know how old the diamond brite is but it was looking pretty good in March.
Chemistry this morning:
pH ? too high FC
FC fell from 30 at 1 AM, measured 24 at 930 AM, got a little sun but not enough to drop that much IMO, something is living in the pool. There is a small bit of organic material on the floor, I have yet to pick up a hose to vacuum so have been brushing towards the main drain, obviously not effective enough. I'm going to pick up a vacuum now.
CH is down from 500, TA is down from 110, CYA is down from 90, presumably from water replacement over the last 60 days. Algae is what it is, but this finish falling off is an issue. I've brushed before without issue, is it possible high FC or high pH is causing this? I adjust pH down from ~7.8 to ~7.5 every two days, rises faster than I like, I'll address that after by lowering TA, started doing this 2 weeks ago by acid lowering and aeration, got it down a little and decided to wait to do it again. When I first started SLAM Friday I added acid to take it down to 7.5, did not see the comment to lower to 7.2 first, so last night I added 16 oz MA to keep it down. I see high FC makes pH drop test inaccurate, I have an electronic pH meter, will this be accurate?
Please see the following link to dropbox pictures showing patches of yellow and erosion at these areas and next to the light. You can also see in the pics the side rails of the ladder are darkening, they always were but I feel like they may be getting darker recently.
Thanks for any help!