What do you do if you are not going to open your above ground pool this summer but still want to next year?

Alage grows with light, hopefully you have a dark cover, just leave the pool covered, if you can put some alage destroyer in the pool when ever you think about it once a month or so you should be fine, however the debris that collects on top of the cover that should not be allowed to build up that's where you get into trouble try to remove or keep it off the cover and uncover the pool next year,