I installed 1 micron bag filters in place of the return eye balls to act as final or clean up filters, and they have been collecting some large debris that should not get though the sand filter. The stuff consists whole ant bodies, leaf fragments, and similar light weight material that floats. All of it is too large to pass though a sand filter and I think even if the filter were channeling it would be too large to pass the screens.
The only explanation I can come up with is the material is short circuiting the sand bed by passing though the space between the internal riser pipe and the slip fitting on the multi-port valve. If the riser was cracked or had a hole I would expect to see sand in the filters, but I don't see any.
I intend to take the multi-port valve off and inspect the inside of the filter, valve, and riser to see if there are any obvious problems. It occurs to me that maybe placing an O-ring around the riser to make a tighter fit between the pipe and the valve might cure the problem if that is the cause.
Has anyone encountered a by-passing problem before, or had any problem with a loose fit between the riser and the valve?
Edit: Here is a picture of the inside of one of the bags. It was in service about 12 hours. I normally leave them in for about two weeks and after that time they have a lot of "stuff" inside that should not be there.