Controlling the algae in your marine aquarium is a challenge that many hobbyists are challenged by. As evidently it is impossibly to prevent any algae forming in your tank entirely. There are many forms of algae that can form in your aquarium, all to which come with their different issues and need different procedures to manage.
A common misconception is that to manage your algae issues, all you need to do is add a algae eating fish or invertebrate. Though this can have its benefits, the downside is that you are now adding more livestock to your marine aquarium to which is then adding to the bioload and without increasing your water (natural seawater, sea water, NSW) changes your nutrients will increase and then feed your algae further.
Usually algae become very problematic when your nutrients are not being exported effectively. To which should be your major concern in defeating the issue. However, this is not to say that algae eating fish and invertebrates are not necessary. In fact, they are a great additional to any aquarium if it is not already overstocked. This is because all aquariums will get some algae in one form or another and having these additions will help keep them at bay in the first place. They should just not be a fix for an issue, just a supplement along with general aquarium maintenance and water changes (natural seawater, sea water, NSW).
Any aquarium is guaranteed to have a certain level of nutrients and lighting, and therefore there will always be a certain level of algae growth in any aquarium. So, any algae eating fish or invertebrate you add will always provide some form of benefit.