Going forward, when dealing with cichlids, it's really important that you only get fish that you:
1. know what it is
2. have the proper tank for it when you get it home
3. have the proper tank mates for when you get it home.
You can throw a bunch of non agressive tetra, cories, live bearers, etc, together and have it not matter. With cichlids, you end up with dead fish.
The fish that's hiding behind the heater is likely to get killed or harassed and stressed to the point he get sick. I've not kept tropheus, so I'm not speaking for direct experience. But more than once I've had to rescue a peacock that was being terrorized, and I didn't always intervene in time, which still makes me feel rotten.