It's going to be next to impossible to accurately measure 20 ppm with the OTO kit, and I have zero faith in the pool store's numbers, so do the best you can until Ben's kit gets here with what you have. ..
The bottle of polyquat is the only type of algaecide we recommend on the forum, so it's not a bad buy--but I"ll let someone who uses it advise you on when to do so--I don't use it in my pool at all.

I doubt seriously your hardness number is 1000 (unless it's total hardness and not just calcium hardness), otherwise with your TA and ph where they are you'd have a pool full of milk. Don't buy anything to adjust it.

And I'd hate to see what happened to a sales person if I told him I wanted a bottle of CYA reagent and he said I didn't want that!!!!!!! Stick to your guns, if you ask for something, insist that they sell it to you--have confidence!!

Janet