You made a wise decision going with the petricolas. I've kept them in the past. Now I'm keeping 4 Synadontis luccipinis in my 40B and they are one of my all time fav. fish. These fish act just like the petricolas but stay a little smaller and have a slightly darker appearance and different spot patterns, otherwise they're pretty hard to tell apart. For some reason, mine only come out when feeding and when it's recess time. They have some sort of schedule and are not always active all day long. They love caves. They have characteristics of a shark
Just watch them swim, you'll see what I mean. Here's a not so good shot at one of them:
Post lots of pics once you get em.