I love the calvus - very pretty fish.
Anyway, I don't think adding a paradise fish is a good idea either. IME, these fish are aggressive when kept in too small a tank with too many other fish. They react very badly to being in crowded conditions and keeping them with territorial tank-mates could be disastrous. If you want these anabantoids (males especialy) to be peaceful, you need to keep them in a tank with plenty of cover, lots of plants and hiding places and areas where they can set up an undisputed territory. Having said that, all gouramies, bettas and their relatives, including these paradise fish, have characters all their own. Each is unique and often you'll find many exceptions to what you considered the rule. There is a small chance you could stumble across an individual that works well in your tank. However, I'd only consider it once your current fish are full grown - I suspect you'll realise then that actualy adding another territorial or aggressive fish to the mix will just result in chaos. If you still think it's a good idea then, re-arange the tank to create new territories and then add one and see how it goes but please watch carefuly in case of trouble - it would be a shame to lose any of the fish. Personaly, I wouldn't think it's worth the risk.