My tangs would not take to algae strips in the beginning, this is what worked for me:
Turn off return pumps. Hold the algae sheet in your hand in front of a powerhead, and rub it between your fingers to break it apart. It will look like flake food floating around being moved by the powerheads. Even if the tang does not jump on the flakes right away, it should start picking them off the rocks. The hope is that over time it will learn that the flakes are in fact food, then that the sheet you're holding is food, and then eventually just the sheet. It's worked really well. I even have my Copperband Butterfly trained to eat out of my hand after using this method. Comes in handy when trying to catch a fish too. It's actually how I caught my evil coral eating Sailfin! Now if only my Hippo wasn't so skiddish and would come up to my hand so I could get him out! My Blonde Naso literally lays in my hand because it's associated it with food, LOL
Side note: My tangs will not eat plain Nori or Green Algae sheets, doesn't matter how I feed it or what brand it is. They LOVE Ocean Nutrition and Julian Sprung's Red, Purple and Brown sheets though.