I get 17000 gallons and a 5 ppm increase in FC for 1 lb of 73% calhypo.
You can use my pool calculator, see the link in my signature to answer questions like this one, though it does take a little more work to go backwards. My pool calculator is designed to go from the desired increase in FC to the amount of calhypo, but by trying a few numbers till you get the weight you want it is possible to go backwards.
bassadict69, did your FC level drop to a low level when the green occurred or are you saying that at a minimum FC of 9.5 and a CYA of 50 ppm you are now seeing green? Did the water get dull and then hazy and then cloudy before it turned green? Did the pH go up before the pool turned green or did you add chlorine before it turned green (could be copper instead of algae)?
I make dang sure not to add anything with metals & got it tested about a week ago & metals came back zero.
FC has not been allowed to drop below 8, I can shock it to 20 for a few days & the best it will do is lighten up a little but keeps the green tint & it settles on the bottom until we stir it up...then it is green again. pH has been holding steady at about 7.4 all season. No problems there.
Phosphates are off the chart due to bad community water. We struggle with this every year until we do a Phos floc, then we are good til the end of the season. We just started the floc tonight & started another thread following the progress.
If you know what the phosphates level is, let us know -- even if it's "at least" some large number. It would be good to know when the disinfecting chlorine level isn't enough to keep away green algae at the normally recommended levels. Though this is one data point, it's a start to figuring out when a phosphate remover makes the most sense.