I just try to keep nori in the tanks 24/7. Get a good nori feeder that makes sure the nori does not get lose in the tank. Some days my 4 tangs plus all the other fish seem to enjoy nori snacks and they will go through 2 sheets in a day in some days and sometimes 2 sheets can last 1.5-2 days. They know how much they need. More @Wikipedia
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