Never ignore checking the pool for a week.
We had a lot going on last week, and left the solar cover on the pool. Every time I walked by I saw it was still blue and said, I'll have to check the chemistry later.
Friday AM, still blue, Friday evening... green.
I'm beating the bloom back into submission, still had some Cal-Hypo to speed up the shocking... but boy, it would have been a beautiful day to swim today!