Do you have a way to help filter it out? Are you running a sump w/ a filter sock? A skimmer would help and a canister or hang on filter would help a lot as well.
why are you adding sand now that you have water in the tank? Just wondering... If this is the way your going to go then i would shut off pumps while adding the sand. once your done adding sand i would turn on pumps add a filter sock and turn on skimmer. Of course this all depends how your setup is...