I have a Yellow Salfin tang and a Naso Tang.
Both Prefer to pick at the LR but as soon as I put a piece of nori in it's gone in about 30 minuutes. I usually put a 2"-3" piece on a lettuce clip with a suction cup near the top of the tank where their is little flow. The Naso is always first in ripping it to shreds then in come the yellow to clean it up. Both of my tangs will not touch the flakes I put in for the Maroon clow and the green chromis.
P.S. I buy the nori at my grocery store, I soak it in garlic for about 20 minuntes before I put it in. To prepare the garlic I took 3 cloves and stuck them in about 1 cup of water and blended it til no chunks were left, ,I then put a cap on the jar a leave it in the fridge.