I have a 10g that was used as a quarantine/baby fish tank for almost a
year, until it developed massive amounts of brown algae. All the fish
have since gone on to longer tanks, and it has just been sitting there
filtering for ages. Instead of cleaning out the algae, I decided to let
it continue to run until the algae ran out of nitrates and starved
themselves to death. The gravel is now back to it's original bright white.

I need ideas for what to do with the tank now. At present I have the
following tanks:

5.5g - 3 tiger barbs, 1 zebra snail
10g - empty
38g - Buttikoferi and Leporinus

In another 6 months the B&L will be ready to move up to their final tank
(probably a 125) which will also give me the 38 to move other fish up
into at some point.

Any ideas for something to do with it? The meaner the fish, the better