with the Hillstream loaches... it's a "Noah's arc" tank... I love that term, another member
@Naughts ... coined, "(This can become quite sophisticated but unfortunately most fish keepers will not put the fish first. Most minimum numbers will be insufficient (6 is not enough for small fish, timid fish, nippy fish and so on) yet the average inexperienced fish keeper will want smaller, not larger group sizes. Maybe this is akin to the ‘Noah’s Ark’ community fish tank where the keeper wants to try 2 of every species and thinks they are then experienced in keeping all of them, when actually they are getting a very poor experience."
in this particular case, they are all very social, I'd expect no differences, if I had 10 different varieties in groups of 3, or 30 of just one species... I try to buy in groups of 3, but there are a couple ( like that red tailed tiger ) that were pretty expensive, & I just bought 2 of them... you can tell by the pictures of the Hillstreams, that have several varieties interacting... in my South American Tetra tank, the various tetras do interact, but most typically swim within the school of their own species...
my goal on this tank, is to set up a new aquarium, & move the Tin Foil Barbs, & the gourami, & let the Denison's be tank boss, & continue to add more different varieties of Hillstreams... ( I had no idea there were so many different varieties, when I started buying them ) I've got several on my buy list, that are only at 1 inch long right now, so much less bio load than the 5 adult Tin Foils