I would suggest Rainbow Fish, but they can be a b*tch in terms of £££ and i am sure with a 6x2x2 you looking for a group of about 6-10 fish i guess (minimum)?
Rosy Barbs
Spanner Barbs
A bit smaller, but Blue Tetra's (i have some) they are mad, always on the move chasing each other, and probably big enough and fast enough to avoid the Salvini i imagine
http://www.petshop-zoomania.com/Tetr...tra%20male.jpg