You can lower the CYA by 50% if you drain 50% of the water. Or...you can just run a high CYA pool, per Pooldoc's guide, which won't waste nearly as much water, and actually will make chlorine additions less frequent for you. Then as the water level is lowered by splashout and backwashing over the summer and topped off with fresh, the CYA will slowly lower itself. Of course, you need to stop using any form of stabilized chlorine (dichlor powder, trichlor tabs, etc.).

You'll need to wait for the chlorine levels to come down before you can get an accurate pH reading....