Live and learn, hoping for a trouble free pool and so glad to have found this site. I ask myself why and how come this aglae happened??Chorine was at slam level when I closed pool last year and all good readings this years opening. Water clear as all get out. I was feeling proud, I only thing I can figure is when I took the cover off I didn’t drain the water off the top trying to save on the water bill. The water was clear because I keep skimming it all winter. I won’t do it that way again, next year I will drain the cover before removing it. Can’t think of any other reason this happened? Can just spring pollen cause this? Live and learn ?