Setting up a brand new tank is one of the few situations where I will run carbon for a few days. Aquariums are made by macines now, machines need oiling, and are often cleaned with solvents. Some of these things can be left in a new tank, being petroleum based they don't rinse off easily, and can slowly leach in to your water. Use a water conditioner that deals with heavy metals as well, once again, residue from the manufacturing process.