Is this the 54 litre tank you mention in other posts?
What numbers of the fish mentioned above do you already have?
Are you looking for a singer fish, group of fish, snail, or shrimp as a bottom feeder?
The only fish i would go for in your size tank would be pygmy corys and that would be dependant on how stocked you already are. You might get away with a handful of other small corys like pandas.
A snail would really be your best bet if you didnt want more shrimp.