You definitely need to do a series of drain/refills to lower your CYA, and I would shoot for about 40 ppm. I don't know where you live and how much sun your pool gets, but it's way easier to add more CYA later if you need it than to reduce it, as you are finding out. At least the good news is that your calcium and TA will drop, as well.

Seeing a chlorine level drop from 9.5 to 4 in a couple of days' time is not that surprising, especially if you have sun on the pool over a long period of time. Your pool will be so much easier to deal with once you finish the refilling!

Janet