You can run some carbon and that will help. However, there is a reason for it to stink. Overfeeding, disturbing the sand bed too much or something is dying in the tank. Some say it could be a sign of some kind of algae outbreak or biological filter is not sufficient. Normal salt water doesn't stink or have an odor. The only time I noticed mine having an odor is when cycling my tank with a dead shrimp, so yeah it smelled pretty bad at first and got better as the tank cycled. It wasn't overwhelming, but my filter socks and poly-filter stank pretty bad.