Well a normal cycle tanks alot longer than 8 days. Just running a tank with nothing in it won't cycle a tank. You need a source of ammonia for the benificial bacteria to feed on. (ie.. fish waste, uneaten food or if doing a fishless cycle using pure ammonia. Usually cloudy water in a new tank is a benificial bacterial bloom and is a good thing. Not sure why that would happen immediately. I also doubt its cause they are stirring up the sand. That would settle quickly. Just do regular, frequent water changes and check your water parameters often.