Awesome royal!!! Mine grinds down hugh driftwood pieces like they're lettuce. The prefilter always looks like it's full of old coffee grounds. I don't know if all royals will do this but, mine splits his time between the driftwood and a big boulder of holey rock in his tank (which he's slowly grinding down to sand). He feeds on potato halves, kiwi, earthworm sticks, earthworms, catfish fillets, crushed land snails, mussels, rabbit pellets, and sinking catfish pellets. Here's a pic of all 18" of him.
There are two oscars in the tank with him. You can see them sulking together in the last picture. It is a 75g, I am working towards getting a larger tank for the three and putting my bullhead and pumpkinseeds in the 75g.