I thought I was doing so well...

If I counted correctly, today makes one full week at your SLAM. That's not uncommon at all. I didn't specifically look back for this, but did you ensure there's no chance that algae could be hiding in a nook & cranny somewhere like a light niche, or ladder rung? They get into or behind those items very often. If you've exhausted those areas, then I have one more suggestion. Check your CYA one more time. If it's 90, your SLAM FC would be 35. If it's 80, the your SLAM FC would be 31. I think this is important because even at night, it you exceed your FC by too much your FC can drop by a small amount. It happened to me several nights in a row before someone finally pointed-out to me that "more is not always better". So just be careful of that and double-check your CYA now that it's been a week. You're only off by a couple drops or so, so you are very, very close. Hang in there!
 
The only thing I haven't done is pull the light fixture, everything else is pretty clean. I'll try to get the time to do that this weekend when I can do it in daylight.

I went ahead and tested for CYA today, and it read between 70-80 (so, round up to 80 iirc). Better than it read at the beginning of this process... it might have helped that I did it when it was brighter outside this time. If that is indeed correct, I might be SLAMing too high, I could only bring it up to 31ppm and save myself a little Cl.

FC currently reads 29.5, CC .5.
 
So the last OCLT I tried read about 1.5ppm loss overnight, so I went ahead and called that a win since the FC was so high to begin with at 31ppm. It's been almost a week now and the pool still looks great, today I read everything and I'm back down to FC 9, CC .5, ph 7.8, TA 120. We had to add a little water this week because of loss to evaporation or a small leak somewhere (I'm leaning towards the latter), and the CYA is reading around 60 now. So far it looks good.
 
Keep I mind that a little leak means a constant "little loss" of CYA and CH over time. Not much at first, but can add-up. Since you've raised the checkered flag for the SLAM, now all you can do is monitor everything on a daily basis to stay within your recommended levels. If FC loss seems excessive in the future (i.e. lose over 4ppm FC per day) and/or your water condition changes for the worse, you should know how to handle it now like a pro. If you have any questions down the road, just give us a shout. Enjoy your day.
 
A week or so later now and it still looks fantastic. We've had a bit of heavy rain and the CYA is now down to something more manageable, I've only had to add a little acid and Cl to keep things within normal ranges. I did add some calcium chloride today to bring the CH up to where it should be.

I really appreciate the help, now I have a much better understanding of not only how to fix the pool but why things were going bad in the first place. I've been bragging about TFP, maybe I'll drag in some converts. ;)
 

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