More words from Bob Fenner.....
Quarantine:
Powder Blues are one of the notorious "ich magnet" species of Surgeonfishes, and should definitely be quarantined for at least a two-week period of time before being introduced to the main/display tank. Even then, they will be amongst the first to show signs of pathogenic or environmental disease should something be amiss.
If you’d like, do consider adding a prophylactic freshwater dip/bath (of a few minutes duration) to the acclimation to quarantine process. It’s advisable to add Methylene Blue to the pH-adjusted freshwater to both increase its capacity for oxygen holding as well as calming the dipped specimen.
Aquariums: Size, Type and Time
This is a wide-ranging, fast-swimming vigorous fish that needs plenty of room. The smallest tank I recommend for their keeping is one hundred gallons. At full potential size of about a foot in length, this would only be six times the length of the fish… not too much to ask for.
Acanthurus species do best in reef aquariums, or at least ones with plenty of healthy live rock. Powder Blues will not survive in a sterile "fish only" setting. About tank shape, less "show" and more "standard" tank dimensions are preferable. Lots of rock to graze on, zoom about is of more use than the room to swim up and down.
The age of the system is important on two principal counts, maybe three. More aged systems are best because they will be more stable chemically and physically, as well as likely having more filamentous algae to graze on. By waiting for six or more months before introducing your Powder Blue, you are likely placing it as your last fish, the proper order of introduction.
Water Quality:
Organics should not be allowed to accumulate in this fish’s tank. Amongst reef fishes that "show" signs of nitrate et. al. concentration, Powder Blues rate up near the top. Oversized filtration, circulation, aeration and skimming, along with the use of quality salt-mix (e.g. Instant Ocean, Reef Crystals, Tropic Marin) and regular water changes are necessary. Nitrates should not exceed any more than 10 ppm; pH should not be allowed to drop below 8.2.
Temperature can play a pivotal role in Powder Blue health. They are happiest in warm water, something in the low 80’s F. If yours shows signs of disinterest in feeding, consider elevating the tank temperature.
Foods/Feeding:
Nutrition or should I state, a lack of nutrition is likely the principal cause of loss of this species in captivity. Too often specimens arrive too starved to recover and/or are placed in circumstances where they cannot sustain themselves. It may seem counterintuitive but there is reason to believe that supplying a "fully nutritional" staple food is of at least as much benefit as being conscientious about having greenery available at all times. I have seen very healthy Acanthurus leucosternon that have been fed only on "Spectrum" (New Life International, Inc.) foods for instance.