my tank is going on 3 years old and I still have some particles in the water,as said above,I believe with the fine sand and strong water flow,it is just something you have to live with...
if there is a way for you to use a canister filter,you could remove most of it....I have 1 of these I used to use
Marineland Deluxe Magnum 350 Canister Filter I used the pleated polishing filter and it did an amazing job at polishing the water,but it is an everyday maintenance job,the filter stops up quickly and needs replaced almost daily,which is why I stopped using it...I'm lazy
keep in mind though,if you use this type of filtration,you'll also be removing beneficial stuff as well,it is a micron filter which removes the tiniest of particles