Let's be honest, there are cases of tiger barbs attacking koi in ponds so the size of the body of water and the size of the other fish is no guarantee. They attack in aquariums of 125 gal + not only small crowded tanks. They will go after (especially in a group) fishes much larger than they are. I've personally seen them do this to a big angelfish. Will they nip less in a big school in a lightly stocked large tank? Most likely, but it still depends on what other species they are kept with. Slow swimming fish with long fins, especially small ones like male fancy guppies but also including fish species their same size and larger, are hard for them to resist, it's in their nature. Everyone who adds tiger barbs to a community tank should be aware of this, that's all we're saying. I think green tigers are beautiful fish and I keep them myself, but in their own tank just to be on the safe side (the added benefit is their school looks much prettier and more dramatic swimming by itself too btw), past experience has proven for me it's the best choice, but here's hoping nobody else gets nipped or killed whatever setup you choose...