rainbow shark, albino rainbow shark, red tailed black shark or if the tank is big enough then a couple silver sharks(bala sharks).
P.S. Make sure you dont get the black shark (looks like a redtailed black shark but the tail is black also) as it is very un mixible espicially with your fish,
also with the 3 smaller sharks (rainbow, albino rainbow, red tail black shark) make sure you have a least one small cave/pot/ or some kind of hiding place so it can make a territory, and only 1 per tank (unless silver sharks), but silver sharks can be mixed with one of any of the other sharks aslong as you have the space,
thanks ian