i think as long as its a carpintis and not a cyanoguttatus you should be fine, though all those cichlids are a lot more aggressive than severums so thats the issue i would see is that he might get beat up on, is it a 4ft or 5ft 120g? if 5ft then the stock should be fine but i think it would be tight in a 4ft tank, and if you havent bought any of those other filters yet then i would just go with the one fx5, that is already over-filtering for a 120 and will give you way more than enough flow and would be a lot easier to maintain, no reason to make things harder than you have to especially when that much over filtration wouldnt really do anything better for the tank, there is only going to be enough beneficial bacteria that can live off of the waste and you should definitely be able to fit that much bio media into the fx5