I did the AA treatment and it worked great. It took a week for the pool to start holding FC, but it finally did.
Then we put 6 cal-hypo pucks in the skimmer and a couple things happened:
1] pool got cloudy
2] stains came back
The cloudiness cleared overnight, and is common (as I understand) with cal-hypo in high quantities. I am learning from this site, and use liquid chlorine and cal-hypo pucks for chlorine sources. I may abandon the cal-hypo pucks (I switched to them away from the Trichlor pucks because of our high CYA levels - we have low hardness and a vinyl liner).;
As for the stains coming back, I found this from the bottom of the AA instructions on this site:
"High ph along with high chlorine will precipitate any metals that are not sequestered out of the water and on to the surface of the pool again. If this happens take the ph back down to 7, or 7.2 and add more sequestering agent. This should lift the stain off."
It would seem our 6 cal-hypo pucks represented an accidental "shocking" so the FC shot up...and the pH shot up from the cal-hypo...does that make sense? I read that cal-hypo has high pH.
I brought the pH down to 7 and added lots of sequestering agent. This didn't work, so I think I'll do AA again....but in the future, per the passage above, it would seem that "high FC + high pH = Stains Return."
Does liquid shock increase pH? Would it be worth adding muriatic acid while (or just before) shocking to help prevent a pH increase.
1] is this the key for me? "high FC + high pH = Stains Return"
2] what's the best way to shock my pool and keep pH low?