Last week I had a CYA of 70 and I felt that I was dealing with mustard algae, so therefore I was at a higher shock level. I just checked my CYA and it is now 60 after a partial drain/refill suggestion to lower it.. Today my FC is at 28 coming down from that high level, but my CYA is 60 with a 24 as the FC shock level...we just want to swim without any body parts falling off...would you do it?