I'd be willing to bet that you have some setteling going on. Those particles are not making it through the filtration system. a 200 micron filter should give you an excellent particulate catch rate. I'm not sure how your system is set up, but I like to point one of my return lines in the tank straight down and one at a 45 degree agle to the side. It varies the current and seems to get things moving. I am using a canister and a wet dry on the big displays, so I have two returns to play with. Another method would be to install a power head where you see dead spots. I really don;t like to have too much crap in the tank, but if it helps, then maybe it's something to consider.
All in all it looks like you are makinhg some serious headway! Great job!