I have a 24" commercial size zip-tie that I use to hang my Nori from my hood door. I don't zip the tie to anything the notch on the zip-tie holds it to the door once the door is closed. The plastic tie then just hangs in the tank and the Nori is held with a rubber band. I try to wrap 2 sheets of Nori every day and hang out early in the morning before I go to work. I add Selcon or garlic to the Nori as well. I have 9 tangs in my tank plus 7 pygmy angel fish so they really appreciate the nori. I buy the Nori at an Oriental store at $5.95 for 50 sheets. This really seems to keep my fish healthy.
I guess I'll answer this even though I don't feed the tanks, My wife does. The Main Display get's a total of 4 sheets a day, 2 around noon and 2 early evening. That tank is home to our Naso Tang, Hippo Tang, Sailfin Tang, Powder Blue Tang, Potters Angel, Foxface Lo & "Lips" the lawnmower blenney. All of them have it off the clip before her hand comes out of the water.
The 75G tanks get only 2 sheets a day. Mine houses my Purple tang, Yellow Tang and a few other small fish that eat it. Have yet to notice if my Flame Angel eats it. My wife's has a Coral Beauty Angel & a Yellow tang as well as a few others that join in. The girl's has a Yellow tang and other misc.
The 38G has no tangs or angels and I'm not sure if she feeds any to that tank.
The numbers and times are fine, just replace "sheets" with "strips".
The 120g gets 3" wide strips and the others get 2" wide strips.
The sheets of nori we get, I can usually divide into two 3" strips and one 2" strip.
I know the inhabitants in the 120g would devour 2 or 3 full sheets per day if you put it in there, but they'd be fatter than little pigs! Not to mention the amount of doo-doo they'd produce!! As it is the Naso Tang is almost as fat as he is tall!!