Thanks Watermom.

My wife tested the CYA at 90, but I tested at 100. This is a tough test for me, as the disappearance of the black dot is a bit subjective. Must any resemblance of the dot be completely gone including any shadowing?

The FC of 39 came from a Pool Math Chart on Trouble Free Pools. It stated that with a CYA of 100 that my "normal" FC should be in the 8 to 13 range, "shock" is at 39, and "mustard algae shock" is at 54. Sorry if I am mixing apples and oranges and you guys do not follow this.