If you read O'Brien, you should look for Richard (Chem_Geek) Falk's threads here in the China Shop, and at TroubleFreePool.com in the Deep End section, and get a copy of his spreadsheet.

I don't have time to get into it now, but there is not an "ideal CYA level". There are necessary levels of HOCl for effective algae and bacterial control. But those vary with CYA level, more strongly than with pH.

OBrien lays the ground work for that, but as far as I know, Richard is the only one who has covered it in detail. My own "Best Guess" chart was, and still is, the *practical* applications of those ideas, which I picked up from OBrien via John A. Wojtowicz, and combined with my own field experience. Richard picked the practical application here, about 10 years ago, and took off from there. He found OBrien, got a copy, and was able to get republication permission for a paper long out of print . . . which is why you were able to find it on his machine.

But, at least compared to the conventional pool industry, the BBB method taught here, DE-EMPHASIZES
the necessity of keeping the pH so finely tuned.
because, as you can see in OBrien, the HOCl levels are not nearly so sensitive as they are in a stabilizer free pool.