I think what your tank is missing is fish or shrimp!
And since you seem to have enough equipment for a much larger tank, uh, why not get a 20L? THERE is where your HC would be at home. Or, even better (and my current wish list item), a rimless 33L 48x12x12!
http://www.glasscages.com/?sAction=ViewCat&lCatID=46