Thanks Richard this is most helpful.

Since I started at a cya of 0 this year and have a 30K+ pool I will need a lot of pucks to get to 40-50. Your analysis also explains the modest increase in cya I have seen to date after 20 pucks.

One advantage of bringing up the cya slowly with pucks, is that the FC that I can maintained consistently is 4.5-8 (depending on the number of pucks used simultaneously) and this is a very effective algaecide at the low cyas seen early after opening. My pool is always green and murky on opening no matter how good the cover is (the joys of being surrounded by large trees), but is crystal clear at the end of 7 days after lots of chemicals and the mega puck approach (no matter how poor the pool company is!). Assuming my cya drops again during next winter, this seems a reasonable approach to recuscitation in the spring.
Thanks again