Two things could be going on. First it does take a few weeks for all the dust and fine particles to settle in a new tank. Second and probably the reason is that you are having a bacteria boom. This happens in the beginning when your tank is cycling with fish in it. It will go away in time on its own. Are you testing your water? What is the ammonia and nitrite levels? If you don't have test kits you can bring water in a bag to your local fish store, they will test the water for you. When you do water changes don't stir up the gravel too much, especially if the tank is new. I was vacuuming all of the gravel in the tank every week when I first got the tank and there was a preputial bacteria boom thing going on. Now I section off the tank and only vacuum about one-third of the tank weekly when I do a 20% water change. There are some good articles pinned to the top of the beginners forum that talk about cloudy water.
