Yes the Platax pinnatus is a large fish. It like all batfish tend to pick at sessile invertebrates. The pinnatus is also traditionally very difficult to keep although, their have been aquarium raised specimens coming into the hobby recently. My local fish store has bought three or four individuals this year alone. I do not have one though and have no personal experience keeping them. It does need at least a 200 gallon tank I would think to grow any where near full size.
James