Learn About Algae Control
in Freshwater Aquariums

Image of discus aquarium
Image of algae in aquarium

This article concerns the control of "simple" algae in a freshwater aquarium. It appears luminous green and is easy to manually remove from surfaces as opposed to some types of "more complex" algae that is brown, blue-green, or red in color and often stuck hard to the surfaces in your tank. Many of the complex varieties are not really algae at all and will be dealt with in an upcoming article.

Algae, while not a true plant, are green photosynthetic organisms that often turn our aquarium green, cover surfaces and generally wreck havoc with both freshwater and saltwater aquariums. We remove them and they reappear repeatedly.

We supply all of algae's requirements as we simulate the natural underwater world of fish.
    First we should know why algae grows so happily in our tank.
  • Your filter contains some type of biological filter media to provide the surface area for colonizing bacteria. The good news is that bacteria "eats" nutrients that are toxic to fish. The bad news is that they turn them into nutrients that are food for algae (nitrates).
  • Phosphates are often present in the very tap water you use to top off your tank during water changes. Phosphates are "plant fertilizer" and encourage algae growth
  • The more sunlight-spectrum light your aquarium bulbs contain, the happier the algae will be. The longer you leave your aquarium lights on, the more "sunlight" algae can use to reproduce.
Controlling algae boils down to controlling nutrients and light

We supply all of algae's requirements in aquariums as we simulate the natural underwater world of fish. The presence of some algae is actually beneficial to the aquatic environment, as algae consume nutrients that are bad for fish and some fish consume algae. A little bit of natural green covering is also attractive. However, excessive algae blooms develop when there is an excessive amount of nutrients (such as phosphate and nitrate) in the presence of proper sunlight-spectrum lighting. These nutrients come from tap water as well as fish waste and debris that decomposes, goes through the nitrogen cycle and begins to "age" your tank.

Establishing a balanced and self-sustaining aquarium ecosystem is the first order of business in controlling algae.

With this in mind, it is sometimes an arduous task to get the right balance using environmental adjustment instead of chemicals to control the algae in your tank. However, simply put, controlling algae is only about controlling nutrients and light.

Overstocked tanks have too many fish for the amount of filtering that is taking place. Because fish waste is ultimately turned into nitrate, too many fish produce too much waste for the tank to remain nitrate-free - a must for controlling algae.

Control excess feeding. Fish that do not eat all that is on their plate so to speak, allow excess food to drop to the bottom. There is sits and decomposes, again ultimately turning into nitrate to feed algae.

When excess algae is present, change about 25% of the water in your tank each week, using a good gravel vacuuming system

Water changes remove nitrates and excess nutrients. Gravel vacuuming removes debris BEFORE it is converted to nutrients for algae. When excess algae is present, change about 25% of the water in your tank each week, using a good gravel vacuuming system that will keep any excess fish waste and debris off of the bottom of the tank.

It is of very little value to take nitrate-saturated water from the tank and replace it with phosphate-rich water from the tap. In many parts of the country, those products are in the actual tap water you use to do your water changes. Reverse Osmosis water takes phosphates, silicates, and nitrates out of your water source BEFORE you introduce them into the tank. However, remember that in freshwater tanks, the exclusive or preponderant use of reverse-osmosis-filtered water will cause trace-elements and minerals to diminish to dangerous levels. You must use additives to re-balance those ingredients of natural water.

Adjust the timing and the spectrum of your lighting. Make sure that your tank is not receiving any direct sunlight or bright indirect sunlight from a nearby window. And put your aquarium lights on a timer; 8 hrs is enough for a fish-only tank - 12 hours for a planted one.

Plants are part of the solution. The nutrients that plants use for their health are the same that algae needs to live. Plants eat first and help starve the algae.

Algae will thrive where plants cannot live - under low spectrum lights. But algae will also thrive under high spectrum lighting. The difference is that plants need high spectrum lighting, and plants are part of the solution. Plants remove nutrients from the water for their own nourishment which helps to deprive those nutrients from algae, effectively starving it.

Use mechanical nitrate removers in freshwater aquariums: de-nitraters such as Marineland Black Diamond Charcoal or Aquarium Pharmaceuticals Phos-Zorb and Kent Marine Nitrate Sponge as well as Microbe-Lift Special Blend. Protein skimmers in saltwater aquariums take the toxic by-products out of the water before they have a chance to turn into nitrates, thus lowering the nitrate load in a saltwater or reef tank.

UV sterilizers kill algae cells. Algae also reproduces more rapidly in warm tanks than cool ones. Many types of catfish eat algae

UV sterilizers kill algae cells. You can attach a UV sterilizer to your filter system and have the advantage of killing both algae and pathogen cells such as ich at the same time. There is very little drawback to using a UV sterilizer 24/7, so it is a great one-time investment. It will ultimately save you a huge amount of time combating algae as well as save a lot of fish by reducing the incidence of pathogens in the tank.

Temperature. Algae reproduces more rapidly in warm tanks than cool ones. Lowering the temperature of your fish-only tank to 78° a good idea. Saltwater and reef aquariums can sometimes go as low as 74° to 76°(depending on the species you are keeping). Algae also grows more prolifically in areas of a tank with poor circulation. "Pools" of nutrients can settle in areas without good water flow. Use power heads with rotating heads or multiple internal pumps such as the HYDOR pumps and wave makers for excellent circulation in your tank. (Don't go overboard. Most tropicals don't like ocean waves).

Algae-eating species such as catfish. Otocinclus catfish are popular due to their small size and algae-loving nature. Plecostamus are also popular, although they can grow quite large and unattractive. Mollies pick at algae and are a colorful way to keep algae from the decorations and surfaces. Chinese algae eaters are popular (and eat red algae as well), but they can often become aggressive as they get larger. Introduce a few of the above species early so that they can learn to forage for algae and keep it under control from the beginning.

Manual removal of algae is sometimes necessary. Use a good algae scrubber to manually scrub the walls of the aquarium (be certain to choose one that will not scratch the glass or acrylic of your tank, and don't grab any gravel into is as you scrub). A few minutes after taking the algae off the surfaces, use your gravel vacuum to suck it off the bottom where it has fallen. You can remove the decorations and clean then under hot tap water and soak in saltwater or even weak bleach for 1/2 hour. (Be sure to rinse ALL bleach off of the decorations, as bleach is deadly toxic to fish).

Don't get so overzealous with manual cleaning that you disturb the tank constantly. This will stress the fish and cause more harm than good. If you need to manually remove algae more than every couple of weeks, you MUST rebalance your ecosystem or algae control will be a never-ending, arduous and stressful job.