My 6.5 metre round above-ground pool has been perfect this year. Crystal clear and chemically pretty-much spot on. Removed the cover two days ago and it has turned a brilliant bright green, literally overnight. I've tried a choc treatment and anti-algae treatment and it hasn't made the slightest difference. Interestingly, my neighbours pool has done almost exactly the same, weird or what !!! My only thought is that the massive combining going on all around us has, in some way affected it. Any advice welcome.