Temp is on the higher side, but I don't think that'd be a big problem. 4" TL is about the size where they tend to get a lot more territorial IME, and I'd recommend separation of the group as squabbling will only become worse as time goes by. Have you tried other foods? Perhaps they're not "into" krill anymore. Beak overgrowth is also a bit of a concern when feeding solely krill.