Depends on the type of algae really. Is your tank still cycling or does it already have livestock in it? If you have livestock, tell us a bit about your feeding schedule. What type of lights and how long are you running them? Do you have a test kit? If so, list some of your parameters. Algae usually comes down to an excessive amoount of nutrients in the water (elevated PO4 and NO3 for example). If you aren't feeding anything and the tank is still cycling, then it's part of the cycle as your parameters spike. If you already have livestock, do some 10% waterchanges twice a week for the next two weeks and cut back on your feeding. It's important not to complete a huge water change because any rapid swing in any water chemistry will have bad results. You can also try reducing your light cycle to eradicate algae. If the tank is still cycling, I would invest in a couple snails/hermits and let the algae take its course.