I usually try to take into account the Minimum Tank Size: Recommendations here...
Saltwater Aquarium Fish for Marine Aquariums: Kole Yellow Eye Tang
but with great maintenance this imo this is a good general rule - I have a small yellow tang in my RSM 250, some think a 65 gallon tank is too small for one, mine seems happy & healthy - not stressed, part of that I attribute to proper nutrition - in my 130D I felt it was to small, but this is just my thinking, if it helps
Minimum Tank Size: 70 gallons
Care Level: Moderate
Temperament: Semi-aggressive
Reef Compatible: Yes
Water Conditions: 72-78° F, dKH 8-12, pH 8.1-8.4, sg 1.020-1.025
Max. Size: 7"
Color Form: Tan
Diet: Herbivore
Compatibility: View Chart
Origin: Hawaii
Family: Acanthuridae