You can't really measure 55 - if it's between 50 and 60, you call it 60. So call your CYA around 120.
I would recommend a no-drain water exchange. You could drain the pool down to about a foot in the shallow end left on the liner, but the exchange is safer. Basically you have a submersible pump pumping out water from one end of the pool (deep or shallow depending on the temp of the fill water vs the pool) and a hose filling the other side. Leave the pump off, measure how much water the pump sends out each minute and you can figure out how much water is being replaced per hour. If your CYA is around 120 then you really want to replace about 66% of it to bring it down to CYA 40 or so. Then your FC levels will be much easier to manage.
Here's info on the water exchange:
www.troublefreepool.com