I believe that is one of those automatic skimmer things. The basket goes down in the skimmer hole and the other piece goes inside of it. Air gets trapped under the edge and it floats. Keeps the leaves out or something like that.
Apologies in advance.... as this may be a very silly question.
Can i just drop this into the skimmer hole next to the pool? At the moment, there appears to be some thing connected in the skimmer hole... cant see how this will 'drop in'. Its dark now so cant get a decent pic. Is the skimmer hole 'closed' when the pool is closed for winter?