For a tank that size a yellow tang would be a good choice, and a kole tang would be even better. Both of them will eat some algae, depending on what type it is you are dealing with. At best they will just keep the amount of algae a bit lower, but it will always grow back. Tangs are not a solution to an algae problem, and since they produce a lot of waste they might actually help fuel the algae.
Basically, get a tang if you want one, but if you want to get rid of algae you need to figure out what is causing it and improve your water parameters.