The Krobia would likely do fine as well if you can find them, though the pH may be on the higher end of their spectrum. Many fish can adapt within reason though. I'd call that fully stocked on a 55. On the heavy side for sure if you get a group of the other cichlid species, which I recommend, as 2 cichlids in a tank rarely works out IMO. Especially if both fish are males, one will bully the other to death after a while. There are exceptions of course but I find this is mostly true. I'd get 4 of the other species, and depending on genders you get, sell some after a while, or perhaps keep them all if you get a male and 3 females.