How long has the tank been set up? Although you're probably underfiltered, even if you don't have any fish in yet, the cloudiness is probably due to dust from your substrate, no matter how long you rinsed it before putting it in the tank. You should have something besides just the skimmer. Either a HOB filter or a sump. Get some .50 micron filter pads and put it in the filter and your water will clear quite a bit. If it's only recently set up it won't be crystal clear for a while. Hope that helps. If it doesn't you'll have to provide more info like number of fish in the tank, how often you feed, water parameter's, size of the tank, etc.