These pics are beautiful.
How big is this tank again? Is this the 40?
Sailfin Tangs tend to get to be big species and need an appropriate home from day one to maintain good immune systems and stress levels. I always recommend at least a 125 gallon tank for the size this fish will grow to. Marine creatures, unlike their Freshwater counterparts, will continue to grow despite their tank size. Remember, they had a whole ocean to grow in before we tanked them. These fish really appreciate a 72" long tank, as by adulthood they can max out at over a foot! This will give them appropriate swimming room and proper the proper amount of live rock will give them ample hiding places, making them feel secure in their home.
The only Tangs I recommend for less than 125 gallon tanks are the Ctenochaetus genus, such as Kole and Tomini tangs. A more seasoned aquarist can probably successfully keep one of this genus in something as small as a 75 gallon, but that is the absolute minimum in my opinion.