I personally would wait before adding any more CYA. At a level of 20 ppm, you should keep your FC around 2 ppm. This will give you some breathing room. Once you get your new solution, test again. In the beginning, I'd test for CYA every other week or so. It was really pointless as I was using only bleach so my CYA would never really rise. I now only test it a week or so after using trichlor pucks (if I've been gone for a week or longer) and at the beginning and end of each season.