You have measureable CC so you need to maintain shock level - there's still a fight in there. Have you measured how much FC you lose overnight? Is your filter pressure climbing? Have you had to backwash it? (only when pressure rises 8-10 above clean)

Don't know why this year is different, maybe the warm winter. Lots of people are opening with huge chlorine demand this year, likely from bioconversion of CYA to ammonia.

(is bioconversion a word?)