Metal Stain Treatment + (Combined) Chorine = Pea Soup Green Pool Water

(I thought I had posted this earlier today, but it isn't showing up in the forum. My apologies if this ends up being a duplicate post.)

My root problem is probably that I shocked too soon after an ascorbic acid stain treatment, but I'd appreciate suggestions on how best to rectify my situation.

15,000 gallon inground pool with 2 year old epoxy surface, zeolite filter. Minor metal staining, probably due to some galvanic corrosion. (Working this issue on a separate thread.) Highest metal reading in early spring, with little/no sequestrant added over the winter, was 0.4 ppm copper. (We don't close the pool.)

Performed standard ascorbic acid (AA) stain treatment. (BTW - 2.2 lbs. of pure ascorbic acid is $17-$18 on eBay.)

Tried to keep ahead of algae before/during/after the AA treatment with Polyquat 60. (There was an algae breakout while the chlorine levels were dropping prior to the AA treatment. Knocked it back with Polyquat 60 and vacuumed the dead critters to waste.)

After the AA treatment I added Metal Trap sequestrant. Also used Metal Trap 2-part flocculant, which is supposed to physically precipitate the metals that were lifted by the AA. It took the predicted 4-5 days for the flocculant to clear, after which I vacuumed to waste.

The water was still cloudy, so I assumed that the algae had broken through somehow. (I hadn't seen some other threads where it is noted that sequestrant can turn the water cloudy.)

Raised pH and TA and then started raising the chlorine using liquid chlorine. As soon as I got measurable chlorine levels I saw that I had 1-2 ppm combined chlorine, which seemed to confirm the algae hypothesis.

5-6 days after the AA treatment I took a chance, put in 2 cups of trichlor and..............instant pea green water.

In for a dime, in for a dollar, I kept adding chlorine - liquid and trichlor - over several days but never was able to reach breakpoint. Could the combined chorine reading be an artifact of the AA treatment? I also dumped in a half gallon of Natural Chemistry Metal Free that I had.

Last evening the chlorine levels were >10 (higher than my LaMotte ColorQ can read). Water was still pea soup green.

This morning the water is now clear and a light blue-green. Can't yet tell if there was any (re)staining of the walls. The PVC fittings are stained, and there is some staining on the wall where a return jet water flow runs parallel to the wall.

Current readings are:
** FCL - 0.67
** TCL - 1.75
** pH - 7.0
** TA - 152 (target is 125-150 per epoxy paint mfr. recommendation)
** CH - 165 (target is 175-225 per epoxy paint mfr. recommendation)
** CYA - 19 (left it low to allow quicker drop in chlorine after shocking / due to high CH did a 1/3 drain/refill of pool before starting AA)
** Cu - 0.0
** Ir - 0.0

Questions:

** Is the combined chlorine reading valid or an artifact of the AA treatment?
** If valid, how can I hit breakpoint without (literally) going back in the soup?
** Does the rapid drop in chlorine from last night reflect anything other than the low CYA?
** Should I take advantage of the low chlorine and low pH to do another AA treatment? There should still be a mess of sequestrant in the water. I also have a CuLator metal adsorbant in the lint basket.

Thanks!