Just noticed my algae Benny looks very skinny. I have him about 10 weeks and have seen him picking at the liverock. All my other fish seem to be fine and well feed. I currently feed dried nori , pellets, flakes and various frozen foods. The tank has about 150 kg of rock for grazing. Any ideas ? ?

I would try to put in a veggie clip with some algae clipped to it just to make sure it has enough to eat.. Just do it maybe once a week or so.