Keyholes (
Cleithracara maronii) are beautiful fish, they are quite shy, but a lot of people don't seem to realise that they are also pretty boisterous once they know their surroundings and tank-mates. At one end of the scale they can be very skittish, swimming away to hide as you walk up to the tank. Then at the other end of the scale they then become inquisitive and will swim up to "greet" you. What's funny about them is that this happens pretty much straight after the first "end of scale" example I gave you, they are quite mad!
You might find this page useful:
http://cichlid-forum.com/profiles/species.php?id=139
They are pretty easy going fish, they are piscivourous, probably more-so than most people expect. This means that smaller fish can be at risk. As I mentioned earlier, the Keyhole can be quite boisterous and inquisitive so even at a small size they will try to chase down smaller fish (big eyes for their stomachs). My guy is still only small at 3" or so, but he is very brave and was the only fish that would stand up to my insane male Bolivian Ram, which not even my Rotkeil would stand against! He lives with the Rotkeil and a couple of P. taeniatus in a 55 and gets on well, he is the second king of the tank, even over my dominant taeniatus male (who you don't want to screw around with!).
So, they are great fish, easy to care for, just provide plenty of cover for them to feel comfortable, my guy really appreciates oak leaves to flip over and hunt for food. Medium soft- soft water with pH of up to 7.5 is fine and don't over feed them! They are REALLY good at begging for food. Driftwood is always appreciated and avoid small fish. Keep an eye on the Red tail black shark (
Epalzeorhynchos bicolor) as they can get highly aggressive as they mature, beautiful fish, but can be right buggers. Just in case you weren't aware. The other fish should get on fine.
What size tank (presumably the 84 gal in your sig?) Do you have any other fish in this tank? You could have more than the one keyhole in there, depending on other fish and footprint (of the tank) you could have 2 pairs, leaving adequate room for when they attain their full size...
HTH
Blair.