[Myka]

If the tank is only 3 weeks old it shouldn't have fish in it yet. Does it have live rock or dry rock? How many lbs? How big is the tank? How did you cycle it? Have you tested ammonia and nitrate? Th cloudy water is probably due to ammonia. If the fish remain in this water they will get ammonia burn on their gills, and will probably succumb. What fish and how many did you add? The skimmate from the skimmer should be green and smell awful.