Richard, thanks for the pointers on the spreadsheet. I presumed it would be complex, but your very lucid explanations of what seems to be happening with pool water has rekindled my long-lost chemistry interest (lost after too many late evenings studying for quizzes). I'll use at my own risk!

smallpooldad, I've found that directly applying (rubbing/scrubbing) tri-chlor onto black algae patches seems to work quite well. And I've been using a stainless steel brush on mustard algae with good success also; the stainless brush seems to work better than a synthetic bristle brush.....but just my experience.