Tropical fish tank help?

i bought a 40gal tank from petco and it came in a kit with the heater and penguin 200 bio-filter, i washed off about 60pounds of gravel and then put that in, followed by a piece of washed off drift wood, then i filled the tank with tap water and put 2 packets of the tetra-care stuff in to make it safe for the fish, 6 hours later i went to walmart and bought 2 fish , a bala shark and a clown loach to see if they could survive, being walmart fish and all, anf they died the next day, so i went out and got startright chemicals and ph balancing tablets and added the right amount, then today i added 2 new fish from my local fish store, my question is, why is my tank so clouldy? and why does it start to have a smell? i didnt over feed, and is it just the new tank and i have to wait? the new fish are a catfish and a redtailed shark