I've panthers in my predators tanks and large fish tanks - nearly in each tank large enough for them. IMHO, 400 - 500l is a minimum-optimum. This fish, when young, will successfully set even in the 100 - 200l, but in a few months it will overgrow... It's not a pleasant sight - 20cm grouper in a 150l tank

IMHO, this grouper is one of the most compatible with other fish - together with Variola louti, they're two of the most peaceful large groupers. Others, like Cephalopholis, Epinephelus etc - are enormously agressive, territorial and in a very short time will kill every other fish, even triggers and small sharks. Pogonoperca, Diploprion, Grammistes etc are not so "clever" and "sociable", and also may be very shy.
And, essentially, average size of tankmates must be corresponding - no less than about 1\2 of the length of a grouper for high-bodied fishes (e.g., Platax) and no less than 2\3 for others. In fact, no fish of such predatory origin can sucessfully coexist with small "reef" fishes - they're just do not consider them to be FISH :spin1: - nothing but feeders :eek1:
And one more moment - IMHO, the best way to settle successfully such territorial predator in a tank is to put him there in the last turn, after all other fishes had settled and recovered. This may be not so essential for concrete (calm and peaceful) specimen, but is very useful in general.
As for Cromileptis itself - it is one of the most thankful, peaceful and sociable fishes, becoming fully tame in a few months. It's very easy and nearly completely safe (! - can occasionally bite one's finger, but only occasionally!) to feed this fish by hand. Sometimes they like even to be palmed by the owner, or like to rest for a while on a palm.