Look inside your tank about an inch or so down, where the water level is now. There's silicone around the entire inside where the trim meets the glass. It might be under a lip so feel under there with your finger if there is one. Or fill the tank back up and watch where it's leaking from.
*EDIT* honestly it's probably not that big of a deal if you don't mind your water level right there.
*EDIT* honestly it's probably not that big of a deal if you don't mind your water level right there.

Were the fish eating refried beans?