Look for the thin, kind of spagetti like green stuff. My fish used to like that a lot. Usually you can find it attached to small rocks. I would just rinse in a bit of tap water, then toss into the tank. Tangs would suck it up like spagetti. You can also keep it in some saltwater in your frig for a week or so. Maybe longer if you change the water on it once in a while. You could also possibly dry it out and feed in the future.