I'm sure your issue has been resolved by now but just in case...
Not to delve too deep but I'll give you a little secret on 'cheating the system' lol
When I first added playsand to my 16 gallon I received the same effect, even after washing/rinsing for hours for just a couple inches of sand. The fine particles floated around for about 48 hours, beyond that any stirring while the filter was going would send some of the not-so-fine but fine enough to float particles into the filter which eventually led to it dying completely, even after numerous attempts at completely disassembling, washing, and removing all the sand.
I went out to my local big-chain LFS and purchased a new one, saving the receipt and supplied filters/biowheel. I then cleaned the main unit of my original filter with vinegar removing any salt/hard water deposits etc and placed the NEW supplied filter cartridge (still wrapped) and biowheel on my OLD unit and put it back in the box. This may seem like overkill because I think my model was still under warranty but I'm not sure my LFS would accept the return or exchange on a unit well over a month old. It certainly seems sure-fire.
The only reason I say all this is, I have corydoras which for the life of the aquarium always stir up the sand jetting around the bottom and pushing it around. It seemed best to kill the original filter and let it remove all the fine particle sand and sediment that over time could kill my second filter. Any remaining sand in my aquarium now seems to heavy to be suspended in the water column long enough to be sent into my filter jamming it up.
And everyone knows a filter is the last thing you want to go up in smoke while you're out all day at work.