Keeping the aquarium clean and smelling good!

We just added a couple goldfish to our tank about a week and a half ago and ever since it has really started to smell. We recently changed the filter as well but that smell does not seem to go away. It also is a bit cloudy in there. Any suggestions on what else I can do to make that smell go away and keep the water cleaner? None of the fish seem to be effected by it thankfully.