I was working on the assumption that he wanted more fish than just two convictsA 20L is generally considered a good size to breed cons in with proper hiding spots.
As for rams, they like soft, acidic, *clean* water. They will not thrive in hard alkaline water, and they'll be miserable if water changes are neglected. Suitable tankmates would be smaller, peaceful tetras, barbs, or rasboras (tinfoils don't qualify as "small"), as well as cories and the smaller plecos (peckolita, ancistrus, etc). You could keep a couple dwarf gouramies with them too, I guess.