I get mine at Cub Foods, but it's standard Roasted Seaweed Sushi Nori, 10 calories and no fat!! For what's it's worth, I just read the package and there is only one ingredient: Roasted seaweed.
My tangs and lawnmower blenny love it. Although I will say that when I first started it, i did add a couple drops of garlic oil from a garlic pill. I don't do that at all any more and they eat it up quickly.
To serve, I cut (i.e., fold) a sheet in half. Put it on a plate and splash it with tank water, then I soak it for a few seconds until it is soft all over. I then fold it in half lengthwise, then again, and finally a third time. I place it on a clip in my tank.
I used to have a suction cup clip stuck to the side, but my snails kept eating all the seaweed. So, I put a plastic tie across my middle brace and hooked the clip to it. Try to position the seaweed out of direct water flow or it will tear up the seaweed. Have fun.