For now, I would just shock and maintain shock level for a few days before I worried about cya.

Then, after your water clears up you can adjust your cya. If it were my pool, I'd not use the pucks. I would just add a little cya. Since you aren't sure of the exact reading, you'll need to go slow. I would add enough to the skimmer while the pump is running (per label directions) to raise the cya by 10 ppm. Then, wait a week to let it dissolve completely before retesting it. That way you should be able to get a more accurate reading. Then, if it is still too low, you can add more later. (Also don't backwash for a week.) Other people prefer to just use the pucks to slowly let the cya rise. It is just a matter of preference. If you do decide to use the pucks, just monitor your cya level every few weeks.