Did you rinse the packet out good before you put it in. May be dust from the manufacturing process. If it's "fines" or dust fron the media, it will be inorganic and shouldn't affect anything. Just annoying. If your filter pad can't get it out because it's too fine, get a flocculant like API Accu-Clear. Here's a link with info on what it does. Good luck, been there. OS.
API Accu-Clear at PETCO