What to do about particles floating in pool?
Is the skimmer basket unit working properly so that the pump sucks in water from right at the water surface? If not then repair or replace it with new parts as necessary. 

Your DE filtration system may have some problems. The internal screens that hold the DE matrix in place may have holes that allow water to go right through the filter without passing through a layer of the DE material. If so then the problem screens would need replacement.

It is also possible that the last time the filter system was replenished with DE material that not enough was added and so some portion of the filter screens are not covered with a layer DE material or the layer is way way to thin. In this case your planned back flush and maintenance check of the filter is in order.