I'm now shocking the pool, trying to maintain 10 or better even though I'm not sure of my CYA yet. I did test overnight last night, and I used about two points of chlorine (36 oz, 10% concentration) between 9PM and 7:30 AM, all sun-free time. During the day, in bright sunlight, I'm dropping the same two points in about an hour, so that makes me think the CYA is still pretty low.
A couple of (almost) clear shots of the algae/stains remaining in the pool:
First, the southwest corner of the pool, which gets the least direct sunlight. The whole south wall has a little of this near the floor-wall junction, but it's the worst where this picture was taken. Trichlor doesn't seem to have much impact. I'll be trying vitamin C today.
The floor on the west end. This looks like brown dirt stains, but trichlor cuts it, and vitamin C does basically nothing. The east end gets more sun and except for the southeast corner is almost completely clean. Is this the dreaded yellow algae? The stuff on the west wall (on the right) is mostly black, the stuff on the floor (left side of picture) is shades of brown.
I'm brushing a couple times a day and just vacuumed this morning for the first time, since all the leaves are gone. There was surprisingly little loose dirt on the bottom, I guess because I used a fine-mesh net bag to get most of the garbage out and brought a lot of dirt up that way.
I'm going to take another CYA reading this evening and see where I stand.
Oh, and here's a picture that shows the overall water quality. Compared to where I started (see page 1) the difference is amazing, but I've still got a long way to go.
Oh, and a general question I might be better asking elsewhere in the forum: Where's the "sweet spot" for a chlorine pool as far as CYA? Has anybody done a curve that says at X level of CYA, your chlorine consumption will be at its lowest? All I know is that's somewhere between 30 and 100. :?