Hi there new to forum have been reading as much as I can about swimming pools. I am trying to find out about different types of pool vents. OK don't laugh I'm new to this. The house I am buying has a bunch of pop up where the water goes into , I was told by owner that they help keep pool clean? Anyway pool is green and pop ups do not pop up so guess I am wondering is this expensive to repair and how it would actually works. Hope anyone can help would be greatly appreciated.