Even though I'd brushed it, my pool screen roof still had a lot of live oak blossom on it. We had our first storm for ages yesterday afternoon and my sparkly blue pool went to this within minutes
Started the pump and filter and it went to this within 10 minutes
About an hour later, sparkly blue again! I did take FC up from 7 to 16 just in case. Moral of the story, clean your screen!