Algae, the bane of every aquarium keeper, has its way with every existing healthy aquatic habitat on the planet, whether it's your aquarium or the ocean. As difficult as it may be to understand, the presence of algae does not suggest that the aquarium is dirty. There is no safe way to completely stop or prevent algae growth. The growth of algae is a result of the presence of light and nutrients in the water. Algae will normally begin its growth back into your aquarium within about three weeks of cleaning it and removing every speck of algae that resides there. Since you have cleaned away all existing algae, you have also removed competition for nutrients in the water that returning organisms will feed upon. However, there are several ways to help control the return of algae to your aquarium.
Clean your aquarium, but push aside a few algae-encrusted rocks or corals. Don't remove any of the algae from them. Appoint them to be the designated algae police, and hide them behind other ornaments or plants if their appearance disturbs you. Your pet algae rocks will consume nutrients in the water, and will help to control the appearance of new growth elsewhere in the tank by getting to the available nutrients first.
Find out if you've been overfeeding your aquarium. Feed the same amount of food that you usually do, then watch the fish eat. If some of the food is falling to the floor of the tank, you are overfeeding your fish. Feed them a little at a time instead of a single offering. Drop in a few flakes, and allow them to clean it all up. Then drop in a few more flakes and make sure that they finish all of that portion, too. As soon as you see that the fish seem to lose interest in any more food, or they mouth it and spit it back out, stop feeding them. If you've been feeding them “just a pinch,” realize that it has probably been too much. Fish are cold-blooded, and require much less in the way of food than warm-blooded animals do. Controlling the amount of uneaten food in the aquarium will go a long way toward controlling algae regrowth by depriving them of excessive nutrients.
Remove dead fish and plants from your aquarium immediately upon sight. Decomposing materials produce high quantities of nutrients in the water, providing algae with food and facilitating their rapid growth.
Reduce the amount of lighting your aquarium receives every day. Move it to a darker area if gets even indirect sunlight from a nearby a window. If relocation isn't an option, shade the tank by closing draperies or blinds during the day. Leave the aquarium lights off, and don't turn them on until evening. Fish require at least six hours of light daily for their bodies to manufacture sufficient amounts of Vitamin D. They also need for the timing of lighting to be consistent, so turn the lights on and off at the same time every day. Providing no more than ten hours of light during any 24-hour period will help control the growth of algae.
Add one algae-eating snail to your aquarium. Don't keep more than one at any given time, as they may breed and quickly overrun the tank. This creates a huge nuisance population which is more troublesome than the algae is.
Introduce several small plecostomus or other algae-eating fish, which helpfully consume some of the algae. Make sure that the plecostomus species you choose remain small when fully grown, because some of them can become quite large and outgrow your aquarium. Don't depend solely upon them for algae control, however. The fish that feed on algae don't eat it exclusively, and will ignore it altogether if they are otherwise well fed.