Its only based on observation but I think they are social creatures. I have a five-gallon I put one from the main tank in just for algae control, she wasn’t very happy much less active with occasional bouts of frantic swimming, when I put in four more she was back to normal. They actually groom each other and sometimes hang out together for hours on a piece of wood so I am guessing they are much happier in groups, they push each other around sometimes so they probably have a pecking order too. I don’t know about the bio load question, they do lots of poo when they are eating heavily, they seem to go in spurts of eating furiously for a few days then just hanging out doing very little. Most of what they eat is veg but they will eat anything, live bloodworms or water ‘wood lice’ flakes mussels. I don’t think they are anything like as heavy on bio load as fish of a similar size though.