I, too, have a sailfin tang and he eats like a pig. He/she has tripled in size since I got it about one year ago. My tangs love romaine lettuce. They devour on whole leave in a day. However, someone suggested in this forum not feeding them romaine so I switched to nori. Once in a while, I give them lettuce and they still love it.
120 Gal FOWLR
1 Yellow tang
1 Blue tang
1 Sailfin tang
3 chromis
1 cleaner wrass
1 tomato clown
1 sleeper gobie
1 scooter blenny
1 bicolor blenny
1 coral banded shrimp
1 sandsifter star
Emerald crabs, snails, blue and scarlet leg hermits
Wet/Dry filter w bioballs
5+” DSB
Ammonia 0, Nitrites 0, Nitrates 0, PH 8.2, Salinity 1.024