Just a post to maybe let us expand our understanding of algae control.
Last week was really hectic with two grandkids having baseball tournaments and trying to get some things done at home, so I neglected the pool. Wednesday evening, I had a little time to spare so I went out to check the skimmer basket. Nothing there, but I was a little surprised to see that the pool was cloudy enough that I couldn't see the drain 8.5' down.
I immediately raised my chlorine to shock level after figuring out that rain water and backwashing/draining had dropped my CYA by more than 10ppm. Took the dog off the timer so the pump would run all night. Went back out right before bed and replaced about 3ppm of chlorine and hit the sack.
In the morning, I was only down a couple of ppm, but what was really surprising is that water clarity was much better. I could see the slots in the drain cover in about the same light where it was invisible the night before. Even more surprising is that the water was almost clear by 4:30 that afternoon, and was back to very near sparkling by Friday morning. Less than 24 hours from cloudy to clear, and 36 hours from cloudy to sparkling seems almost impossible to me.
I believe that I happened to catch an algae bloom at a very early stage, and I killed it off with an immediate shock. What is surprising is that the water was back to clear so quickly. It almost seems that the chlorination somehow directly cleared the water, as I would have expected 4 or 5 days to get back to sparkling from the stage of cloudiness I had with my filter.
Anybody have any ideas what actually happened?