Yeah, you're pretty limited in your choices. What else is in the tank?
A 9g is pretty small, and bear in mind that algae eaters are only good for cleaning up the small amounts of algae normally produced, so with a tank that size it's often best just to do manual cleanings. Algae eaters will not keep up with a full scale bloom, if that's what you've got you first need to resolve whatever is causing the algae.