Thanks for all the replies.
I have a DE filter so I doubt I can do much to improve the filtering (i.e. adding a skimmer sock). Maybe the water is not getting filtered as much as needed. I'll try and extend the filter time and possibly open the main drain valve a little more ( I draw 95% through skimmer).

What about those (liquid) clarifiers they sell in the pool stores - do they work? What's in them?

Assuming my dull water is due to small suspended particles - would a floculant help - is that the same thing as a clarifier?

Thanks.