Have you tried adding a small amount of DE to your sand filter to see if maybe that will catch it? Watermom, Carl, and Poconos all do that with their sand filters, with good results. Start with only a cup or so--you only want enough to raise your psi by 1 ppm, and that rise isn't always immediate. Add the DE through the skimmer, give it 20-30 minutes or so, and check your filter pressure. If it rises too much, you can always backwash it out and start again. The DE will help the sand pick up finer particles and may save you some vacuuming time.

Janet