I returned from a week's vacation late Tuesday night and checked the pool first thing Wednesday morning and everything was it should be, FC 8, PH was 75. I had stacked 8 3" tabs in the skimmer and they were just about gone. The pool was clear with no signs of algae anywhere.
It started raining hard later in the morning. By late afternoon when I got a break in the rain I went out and checked the pool and I'm glad I did because the water was almost up to the top of my overflow because it was partially blocked by rose petals that had blown in from a climbing rose bush. Since the storm was supposed to last into the night I added another 3.5 ppm of bleach in case I lost power for a day or 2. At this time the pool was clear as a bell. My timer turns off the pump at 7 PM and back on at 6 a.m.
It continued to rain hard until sometime during the night. On Thursday morning the rain had stopped and my wife came in and said the pool was cloudy. It was mostly visible in teh deep end, similar to the morning after a pool party with lots of kids. I checked the chlorine and it was still 7.5, easily within recommended levels for my CYA which I then checked to be somewhere between 60 and 70 (I wish the black dot test weren't so subjective) which was higher than I like but understandable after my second use of CYA adding pucks this spring.
I began shocking at a 20 PPM level late that morning and to keep it short, my first overnight test lost 3 PPM but this a. m. test showed no FC drop, the algae is gone, and the water is clear.
I had a similar but worse problem several years ago when I went to bed with a clear pool. During the evening we got the rain remnants from a hurricane and the next morning my pool water looked like milk. I posted about it then but there were no causal answers. So here are my questions:
Why doesn't the recommended FC level ALWAYS prevent algae? Can there be so much algae in a storm that it gets overloaded?
Would it matter that the pump was off overnight? Since as far as I know the chlorine doesn't fall out of suspension so don't know why it would mater. I don't want to leave it on overnight just in case the overflow got blocked by leaves, twigs, rose petals etc.. Water behind the liner would sure be worse than algae.
Would keeping Polyquat in the pool prevent such a surprise? I'm especially concerned of something like that happening when I was away. I also now realize that my overflow could get clogged while I was gone although that was the first time in 37 years it had almost happened. What a mess that would leave.
Thanks for any help or ideas.