You might try a Green Tiger Loach. Shortly after introducing a 3" specimen to my 72 gallon tank, all of the other loaches became very skiddish. All of the other fish, Blood Parrots, RTBS, various tetras, steered clear of him until I had to get rid of it. My poor Clown loaches had torn up tails and didn't seem too happy. The Tiger Loach grew to about 5" in the short time I had it and I really liked the colouring of it. Too bad it didn't like the other loaches, but it might do well as a lone loach.