One week post SLAM, and the pool is looking great!
I thought I would do a final summary post for anyone reading this thread who may be in the same situation that I was.
I know now that I had algae AND iron problems.
I thought that since my pool was clear before that I didn't have algae, but clearly that wasn't the case.
For me, the SLAM solved both problems. Once I started the SLAM, the super high chlorine level made the iron visible by breaking down the sequestrant. My sand filter got a ton of the iron (when I backwashed, the water was very brown) and then the polyfill got a bunch of it too. When we were in mid-SLAM, we'd put out Ascorbic Acid onto the stairs and in the shallow end to lift off some of the iron staining, and that worked well. But, it worked only in the area that we directly applied it to.
So now, one week after the SLAM was finished, my pool is clearer than I've EVER seen it.
We do still have light iron staining in certain spots, but I"m going to send out my son with some ascorbic acid in a sock to try and directly apply it to the iron staining to see if it comes off and then let the filter and the polyfill do its job.
A hearty hearty thanks to this forum and the experts therein (thank you @Texas Splash and @markayash for being there from the start, and @mknauss for the help as well). I'm a TFP convert and will happily continue to donate to the site. The wisdom here is definitely worth it.
Oh, and P.S. I think the iron staining was caused by AquaSalt brand pool salt.
Thanks for the update. I have been watching closely to see how you have progressed with your staining. I ended up with a slight algae issue after using about 1 1/2 bottles of Vit. C tablets in a sock. Started slamming immediately. Slam is now complete and algae under control. In retrospect, I am thinking either poor circulation or FC depletion by the Vit C allowed for the algae growth. (Also heavy rains due to high humidity...gotta love that Ga heat!). Totally puzzled me because the FC was diligently held at the high end of the range for my CYA. Anyways...just wanted to say keep a close eye out if you use the Vit C!