I had a pair of brown ones that I caught in the bay who lived in my 10g refugium for about a year. I'm pretty sure they died when I pruned out out the type macro algae they were eating. If he's not happy eating what's left in your tank I'd say start trying to feed him different macro algaes - do you have a refugium? You could start a 10g one with a couple compact flourescent bulbs, grab a few types of macro in the water by the skyway rest areas, and see what they eat.