For a long time my skimmer weir just sort of lay there, maybe feebly flopping around from time to time. I finally got a round tuit, and took a close look. It seems to be made of rubber, and there was this construct at the top that seemed specifically designed to hold a stick of styrofoam or some other kind of floatation assist, and it was empty. So, I cut a piece of styrofoam to fit, and stuck it in there.
I have the plumbing arrangement where the main drain pipe goes to the skimmer, and there's one pipe from the skimmer to the pump. Orienting the skimmer basket different ways lets me pick skimmer only, maindrain only, or both. If it's on skimmer only, there's enough water flow that the weir is pulled down below the surface, but if it's on "both" then the suction is much less and the weir is a little bit above the water surface. It looks like the water is mostly coming into the skimmer in the little gaps between the sides of the weir and the walls.
Is the water flow supposed to be over the top of the weir, regardless? If so, I guess I should trim off some of the styrofoam so the weaker flow will still pull it below the surface?