Wow, 56 is a really high chlorine level, even with that high a CYA level. With chlorine levels like that you are very likely to bleach your liner. Check out the "best guess" table in my sig, and you'll see the guideline that we use, very successfully, around this forum.

You do need to be testing your water daily, and adding enough chlorine to get back up to shock level, although I doubt with the levels that you're reaching that you 've ever come down below adequate shock levels, which would be 20 based on your CYA. If your chlorine granules are cal-hypo, then they'll be fine to use up.

Janet