I would drop a raw cocktail shrimp in there (in a stocking to keep it from breaking up all over the place), or dose a couple times a week with pure ammonia. That way they have something to eat.
The ammonia route is a lot less stinky, and you won't need to run carbon on the tank, either. With the shrimp, you get a lot of dissolved organics, the water stinks and will turn yellow-ish. Carbon will clear it up right away, though.