First, do not use any algaefix or similar substances. These may or may not kill algae, but they may also harm plants (if you have any), and even more importantly, fish. Almost any chemical substances added to the water will get into the fish via either osmosis or respiration, and fish do not need to be stressed (or worse) by such substances.
Second, be very careful about buying any so-called algae eating fish. There are many species of algae, and while some of these fish may eat (partially or close to all of) certain species of algae, they will certainly not eat all types. And some of these fish can get quite large, and some have nasty dispositions, and all have basic needs for this or that environment and habitat--and so forth. The answer to any problem is almost never another fish species.
Now to algae, briefly. Algae will occur in any body of water if nutrients are present, and in the presence of light. Some don't even need much light. But my point is that algae is natural and normal, and in a healthy aquarium with fish it will be present. However, we can keep it under control. If you have live plants, we follow one set of guidelines. In the absence of live plants we can be a bit more extreme with the light (intensity and duration both factor in to this equation). I and other members should be able to offer some suggestions, but first we willneed to know data about your aquarium. Light specs, tank size, fish, live plants.
Byron.