chlorine disappears within 24 hours

[RKM]

I am having issues with my swimming pool. My chlorine disappears within 24 hours of adding 4 cups of granular chlorine shock. All the chemicals are perfect, however, my CYA is at 150. I drained 1/3 of the pool, the CYA came down to 100, however, same issue.

Any other thoughts? I am assuming this is a CYA issue.

[chem geek]

You may have nascent algae growth consuming your chlorine. Read this link and note that you should lower your CYA level even more if you want to get ahead of the algae by shocking with chlorine (and for long term as well).