And they are not just odd cases. I opened to green slime and in 24 hours was 90% clear. In a week, I was crystal clear. Why? I didn't panic (I knew why I opened to algae, and what to do). I looked at my wife, shrugged, and she said: "You know what to do better than almost anyone."
It's just not hard to do if you follow the rules, and rule 1) is: You need lots of chlorine, and it's best delivered as bleach or liquid chlorine (same stuff, only more concentrated.)
It works!

Carl