Lisa, she did say pH was high and that she thought it dropping caused the apparent bloom. Also that she maintained pH between 7.8 and 8.2 all summer.

If your pH has been that high all summer, then unless your FC was at the TOP of the recommended maintenance range for your CYA, or higher, then you've been, in my opinion, lucky not to have had a bloom sooner. If your borate level is fairly high and you regularly put in Polyquat 60% it may have inhibited algae growth. Or you just may have been lucky.

But if your CYA is 60 and your FC fell to 5 while your pH was 8 or higher, those numbers work for an algae bloom. It's easily within the range of probability. And once it starts, a normal maintenance range won't stop it.

Now it is also possible you have a lot of pollen, and frequently the stuff is yellow. Allergy season is back on us with a vengeance and even I, who have fairly few allergies, have been suffering.