Instructions
Consider whether the algae is serious enough of a problem to clean. Algae is not necessarily a bad thing, but rather a healthy part of the aquarium's environment; it consumes nutrients that, if left to accumulate, can harm the fish. Only clean algae when it becomes a serious issue.
Apply an algae-scraper to the sides of your tank--one that doesn't damage your finish--and siphon or filter out the dislodged particles. Remove your aquarium's decorations and fake plants, wash them off thoroughly with cold water, and return them to the aquarium.
Do not scrub your aquarium until it is algae-free, but rather leave some behind: a totally-cleansed aquarium can actually produce algae even faster. Even after a good clean, a normal, healthy supply of algae should reassert itself after 2 weeks. If it returns faster than that, in mere days, then you need to reconsider the layout and structure of your aquarium.
Add some plants, if you haven't already. Plants will compete with the algae for nutrients.
Consider adding algae-eating fish--like plecostomus catfish--to your aquarium's population.
Change 10 percent of your water a week, to help prevent severe algae build-up.
Ensure that your aquarium avoids ideal algae-growing conditions. Check and clean your filter regularly; wash it out with water from the aquarium, to preserve the beneficial bacteria. Don't overfeed your fish (which leaves behind scraps), and avoid excessive sunlight.
How to Clean Algae From a Fish Aquarium
Algae can be the bane of an aquarium. It is also, as it turns out, inevitable: if allowed to grow unchecked, it can overwhelm the aquarium's inhabitants, to both their detriment and their owners. On the other hand, if your aquarium is maintained responsibly and carefully, your local algae crop can stop being a scourge, and instead become a benefit.