for a 5 gallon, you realy cant do much.... when you speak of algae... do you mean neusence algae, diatoms, coraline?
one small snail like a nassarious might be okay, but in reality, your best bet is just lowing nutrients and waiting for your tank to mature. That will fix the problem and also once your tank matures and your algae level goes down, you may not have enough for a snail to eat.