The fact remains though Sonic that you really need to:
A - Give them more room to grow into
B - Should keep more than two in a group
The reason the Silver Shark seems to want to hang around with another fish that they too should be kept in groups and need numbers to feel comfortable in their surroundings.
Yes I know, but once my back living room has been decorated i will be looking at getting another (bigger) tank for in there, but that will be quite a while off, but at the moment, they should be happy enough (and seem happy enough) in their current tank, with them only being about 3 to 4 inches between them
Its the silver shark im not sure what to do with at the moment, or when he starts to get too big for the tank, plus I take your point about them also being a schooling fish, he may end up going back to the LFS
Steve