You definitely need more rock in there. If the "brown stuff" is powdery, it's most likely diatomes. If you ever decide to go bigger (or even if you don't), a small RO
system will most likely be more economical than driving to the store and buying jugs of water (not to mention a lot more convenient). A basic RO
) can be gotten for as little as $90 at BRS (Reverse Osmosis Systems - Bulk Reef Supply
), and even less during a group buy (I plan on running one in a week or two).