A plastic drywall knife is probably the cheapest and easiest way to remove algae from the side glass. If you don't want to get your hand wet you can spend a chunk of money on some good quality (strong) algae-scraping magnets. The cheap ones work too, but not as well.
To prevent algae, you can either reduce the light or increase it enough to support "higher" plants that will use the nutrients the algae grows on.