Cool Graeme. Do they have the big nasal nares?
If so they are
P. cuneovirgata, which from your pics I'm pretty certain they are. I just broke down the 30 that mine were living in and found only 1 from 10 that I had

It's fattened up, but grown little. They seem to stay way smaller than other species.
How's your's doing Robin?
The loner is now in the 120 with two
P. anguillaris and 5
P. piperata.
Nice find. Were they a good price? I just about stole mine for 99c each!
Martin.