Again, the "fine dust" you have is algae and you can't get rid of algae unless you SLAM. You probably have just enough FC to keep it from becoming an ugly green swamp, but not enough to kill the algae. DE filters clog very quickly with algae that is probably helping you from getting worse, but I image that you are having to backwash more frequently than usual.
You really need to SLAM your pool to get ahead of the algae. With a DE filter, this will go quickly, but you will need one of the recommended test kits.
Post up some results when you have them and we'll help you get this thing cleared in no time.