just for the record there are 2 basic types of upside downs.... synodontis type and mystus. the upside down catfish "synodontis nigriventis" is a great fish, stays relatively small (maybe 4"), and likes to school. it's not an aggressive fish and likes to hide. it's also usually like a mottled brown color. but you probably would be better with cories for a 10g....
the asian upside down cat "mystus (somethingorother)" is a beautiful fish, but a pure predator. it is mostly black except a few speckles on the sides usually. it will reach 12" and smaller fish won't be safe. it also tends to hide, and is a solitary fish.....