that would be way too small! i would say at least a 20g for a pair of convicts. they are territorial, and like all cichlids need a resonable area of space.
check out mft's freshwater profile for some info:The fish pairs readily, are intolerent and bite. They eat plants. Couples form a patriarch/matriarch family and both care for the youngs. Not recommended for a community tank. Needs a tank with a gravel bottom and hiding places in rocks or inverted pots. Suggest a cover of floating plants.