RBP deffinatly dont need companionship, though often times they are even less active when kept solitary. a buddy of mine has had one by himself for 2-4 years, doin just fine.
as a matter a fact it is better to keep one P alone as opposed to having multiple fish in too small of a tank.
furthermore (though not mentioned) it is better to have one RBP solitare then to have two, as with only two Ps they will fight often as there is no extras to divert attention.
always keep one P or 3 or more
Hope I helped some
Quinn