There are more than one species of commonly named pink tail Chalceus. Their behavior can vary depending on the species as discussed in these threads.
I had a tank with adult veija and added adult Checleus that worked out fine. Tried with some juvie's and had a disaster. Growing out some fish in a 55g. Group of juvi cichlids below , 2-3 , inch. Added School of Chelceus 2-2.5 inch. I thought the Chalceus woud be fine as could not fit in the...
www.monsterfishkeepers.com
I remember way back when I got my Charlie. The stuff i'd read hinted that they were predators and that they'd take small fish if the opportunity presented itself. But mine never bothered any other fish. It just lay still at the top waiting for food to drop in. More reassurance, yay! For...
www.monsterfishkeepers.com
The yellow fin species you have is less conspecific aggressive than the Macrolepedotus species. I currently keep a single individual of both species in my 6 ft tank to avoid conspecific aggression. In my observation of Macro Chalceus in giant public aquarium tanks, they are always cruising solo away from one another. In small dealer tanks, juveniles I observed are always attacking one another with broken nose from jaw locking. Yes, keeping 6 or more individuals will spread out the aggression, but for fish that can reach 12 inch, you need a tank much bigger than 6 ft.