To elaborate on the Tang question.
The biggest issue comes when you try to mix 2 Tangs of the same Genus in an aquarium. Acanthurus tangs and Zebrasoma tangs tend to mix well together, especially if the Acanthurus is larger in size. There are othe Genus of tang, but they are less common, with the exception of the Kohl Tang, which is much less aggressive.
The Zebrasoma's all have a similar body shape to the Yellow Tang
, so you can recognize them easily. The Purple Tang
, Sailfin Tang
, and Scopas Tang
are good examples. Zebrasomas are much better suited for mid sized aquariums, say 75 gallons and larger. They are also the best choice for a reef setup, being rather effective at eating hair algae. Finally, they become very terrirorial in an aquarium and are best added last to a community tank. For larger aquariums, adding multiple Zebrasoma Tangs at the same time is usually successful.
The Acanthur Genus are much longer in body shape, such as the Powder Blue, Powder Brown, and Sohal. The Blue Hippo has a Genus of its own, but it behaves like an Acanthurus after it adapts. The Acanthurus need much more swimming room and you should be prepared for a 220 gallon tank or larger as they grow. Because of their size, the Acanthurus tend to adjust well to more aggressive displays that include Triggers, Puffers, and Large Angelfish species. Keeping multiple Acanthurus Tangs in an aquarium is very difficult, unless the aquarium is extremely large in size, say 400 gallons or more.
For the record, the Acanthurus tangs have an interesting behavior. They often lay on their side, on the bottom of the aquarium, for several days after being added to an aquarium. No reason to panic. This is common. They also exhibit this behavior in the morning when the light is first turned on.