That high of a CYA is gonna be a problem. I'm surprised you don't have a green pool with high cya and no chlorine in there. You have a low water table there, right? If it were me, I'd do a big drain and refill. If a place has a high water table, you don't want to totally empty a pool or it can pop out of the ground. This is not such a problem when the water table is really low. If you aren't sure, just don't drain it all but drain a lot of it. That will get your cya down to a more manageable level and then we'll go from there.

Yes to using bleach. It is what most of us on the forum use for our source of chlorine.