My Naso did not eat any of the food I offered for almost 2 months. Luckily, I had a HUGE problem with dictyota, and it cleaned all that right up, so it never lost any weight. I think the smaller Nasos (mine is about 4 inches as well) take a longer time to adjust to captivity. The first thing I saw it eat was Hikari mysis. Didn't like the bigger PE Mysis and would just spit it out. Now it eats almost everything, except it doesn't fancy Spectrum Pellets very much. It also will rip the Nori right out of my hands. If you can get a rock with a lot of algae on it, this would be the best bet to keep yours from starving. Mine still grazes all day on the various algae in my tank after it's eaten all the Nori. Good luck.