Been doing well with this methods for 3 years, never had any major issues, this year has been very good, water looks crystal clear. two weeks ago, I notice this small thin little patch of green layer in the deep end/corner of the pool. Came off real easy with the brush. Now two weeks later, it appeared in the same spot again. I don't think it can be algae based on my numbers posted below but maybe it is. Should I be concerned? I am in New Jersey and will be closing the pool in two weeks.
CH-220 (vinyl liner)
CYA - 70
I know the CYA is a little high but the FC is 7.5 which is within the Minimum/Target range.