What size tank is this for and are you hooking your skimmer up to the fuge. Why are you using that and not a 20 gallon fish tank so you can glue dividers in it. if i may make a suggestion. I would ask the local fish store for about 2-3 cups of sand from one of there fuge running a display tank, this will jumpstart your fuge.... Good luck post in the lighting section the rest of your setup so we can see.
When you get everything set up take the power head out and add your heater you dont want massive flow in a fuge of that design other wise you will be constantly adding sand to your tank and the inlet from your tank to the fuge will add enough movement to all circulation...