OK,
The subject of tangs, what kind and how many, comes up alot. The problem is there are several answers depending on the type of set-up you have and what you are looking for. I am going to discuss having multiple tangs that are reef safe. There are lots of tangs and surgeon fish that are superb candidates for large fish only set-ups, but those won't be discussed here.
How big of a tank do I need?
In general, tangs require a minimum of 48" of lateral swim room as they are very active swimmers and grazers. Hex and corner bow tanks are not as good of a tank choice because the water volume tends to be more vertical, and other than jelly fish, fish do not swim vertically in their normal activities.
The adult size of the fish is important in choosing the right tank for the tang, or vice versa. Of the tangs that are readily available in the aquaria trade, they grow to a minimum of 7" and the vast majority to 10" - 15". The maximum adult size of the fish should determine the size of your tank.
What do I want a tang for?
Tangs offer a wide variety of body styles and colors. They are excellent and active swimmers that add personality and action to your tank. The most important benefit of having these fish is that, in addition to being active swimmers, they are tremendous grazers and agaevores, aka, good cleaner crew members.
What do I feed my tangs?
Tangs eat a wide variety of algae and may supplement their diet with meaty foods you introduce to your tank. Flake food and seaweed are also to their liking. People also feed their tangs broccolli or other green vegatable matter that approximates their plant diet in the sea. These fish atre known for their appetites and have been called a lot of thing, but never late for dinner.
How many tangs can I have in my tank?
The real challenge here is that it depends on how big the tangs are. You can certainly keep two or three juvenile tangs in a 75 - 100 gallon tank, for a while. They will grow and you will need to accomodate that adult growth at some time in the future. This can be achieved by moving to a new and bigger tank, what a strategy, eh , or trading them in to an LFS or some other more suitable home.
In most reef tanks in the 75 - 100 gallon range you can keep two tangs in the 7' - 10" adult size range without too much problem if you mix the genus properly. Anything under 75 gallons and 48" or longer can accomodate one tang. in that size range.
Michael Paletta suggest a much bigger tank than 75 - 100 gallons for three tangs. I believe he has three in his 240 gallon reef tank.
That being said, there are three genuses that generally get along well because they don't compete for the same food source. The three genuses are:
1. Zebrasoma
2. Acanthurus
3. Ctenochaetus
I have experience with three species, one from each genus that get along well together as they are some of the more peaceful tangs. They are the Sailfin (Zebrasoma veliferum), Convict (Acanthurus triostegus), and Yellow Eyed Kole (Ctenochaetus strigosus) tangs and all are very efficient macro algae eaters. The Sailfin and Convict are very good macroalgaevores and the Yellow Eyed Kole is expert at cleaning green and brown PITA algae from the glass and rocks.
There are several species from each of these genuses that can be mixed and matched. Remember that these are generalities and that each fish is different and may become aggressive if it feels it's territory is being encroached. Some individual fish just have bad dispositions and are not good tank mates.
It is my experience that it is best to add mutiple tangs, odd numbers are better, as young juveniles of the same size. In this way they are not predisposed to aggressive or territorial behavior, and they get to grow up together and gain a familiarity that leads to less potential conflicts.
It is critical that you are responsible and provide tangs with the appropriate swim room. You have to realize that a 240 gallon tank does not duplicate the swim territory of a sinlge tang in the wild so we are really providing the minimum.
