Sounds like you're making progress. How much chlorine are you losing between dusk and dawn?

With a sand filter, you could use the DE trick that the other mods do--they use just enough DE to make the pressure rise by 1# and put it into the skimmer to coat the sand. This will allow the sand filter to pick up smaller particles. If you decide to do this, check after you add it to make sure it's not coming back into the pool via the returns--if that's happening, then you may need to investigate the filter a little further.

Janet