Want fresh sushi? Just reach into your tank...
KIDDING.
Anyway...in lieu of the nori (seaweed), the packaged Seaweed Selects which you can get in almost any pet store are a great source of natural and nutritious food for algae eaters. Our tangs LOVE the stuff off a clip in the tank, they tear it to shreds.
Our blue damsel thats in with them waits in the wings for pieces to fall off, and grabs them.