If you are still cycling the tank, I wouldn't worry too much about both the brown algae (diatoms) or any floating matter/discolored water.
The tank is quickly going through various phases while it establishes itself. Patience is the key here.
If you want to use a form of mechanical filtration to try and clear the water, I would use a 200 micron filter sock. Those should be attached at the overflow discharge in the sump, not at the top of the tank. You an overflow your tank if the filter media becomes clogged at the top, whereas your sump should have enough room to allow the filter sock to overflow with no problems.