Have you tried soaking the nori in garlic extract? Up until recently, my algae blenny never touched nori in my tank (tied to a rock, to pvc, you name it). However, after I started soaking it in garlic extreme, my blenny took to it almost immediately. Now that I got it eating nori sheets, I've got green poop floating around all over the place
...but at least my blenny is fat
-Richer