So, your fish tank is turning green. Before you waste money on some kind of crazy  “algae cure”, you may want to know one thing: 




When we go to a lake or river, we see algae all around us; it is on the rocks, the dock, even on the plants in the shallows.  When we visit a huge, public aquarium, there is algae in every tank, and lots of it.  But, somehow, in a rush to have the “cleanest”, most sterile home aquarium, algae has received a bad rap.  Lets take a second and think about what algae is and isn't.  Algae is not dirt, it is actually a microscopic plant.  Plants are good for your aquarium.  So, believe it or not, you WANT algae in your aquarium!  I’ll give you a second to let that sink in, because I know that this statement is the exact opposite of what the 15-year-old expert at Super Giant Pet Megastore Warehouse told you.


Why is algae beneficial?  Because, it converts the byproducts of fish waste (Nitrogen and CO2) into Oxygen using the energy of light (Photosynthesis).  Fish hate waste, and love oxygen, it’s a win/win situation.  In addition, many fish need or benefit from algae in their diets.  African Cichlids and Mollies immediately come to mind as fish needing algae to really thrive in captivity.  Lastly, an aquarium filled with algae looks good.  Now, I understand that this last statement is another “shock to the system”, but that is exactly how nature looks; at the lake or at a public aquarium.  It may take some getting used to, but think, it wasn’t that long ago that an aquarium filled with dead, bleached, white coral was thought to be good looking, and nobody would have a display like that nowadays.


There are several types of algae that can be grown in an aquarium, some more beneficial than others:


Blue-Green Algae is actually not algae.  It is now believed to be a type of bacteria that uses light. It is seen as a bluish slime or web coating your plants and rocks.  Usually this type of algae is an indicator of poor water quality in an aquarium.  Old textbooks used to recommend the use of antibiotics to kill off this “pest”, but nowadays we don’t indiscriminately use antibiotics for fear of resistant strains of bacteria evolving in the hobby (or even the world in general).  This is one “algae” we don’t want to see, so step up on those water changes, and as the water quality improves, it disappears all by itself. 


Brown Algae is usually seen in either brand new aquariums or aquariums with really old fluorescent lamps.  As a fluorescent lamp ages, the light output falls (50% after the first 6 months) and the spectrum of the light itself changes.  This is why hobbyists who grow aquatic plants replace their lamps twice a year.  A new light bulb will benefit the green algae more than the brown, and allow the green to “take over”.  Another way to grow an incredible amount of brown algae is to use a “cool white” or “shoplight” bulb instead of a bulb made for aquariums.  The spectrum of these hardware store bulbs favors brown algae and can make quite a difference in just a few days.


Hair Algae can be grown in both long and short forms.  It usually anchors itself to rocks and wood and can sometimes grow in clumps over 12 inches long.  African cichlids love to dine on this stuff.  Some hobbyists go as far as to transfer rocks from outdoor “kiddy pools” to their aquariums covered with this algae.  To start a culture of hair algae, attach a clump to a piece of wood or rock with a rubber band somewhere near the top of the aquarium.  In a few weeks, after it “takes root” you can remove the rubber band.  If you find at first that your fish are eating it all before it can spread, you may have to start it in another aquarium, window sill or kiddy pool.   Once you grow enough to reach critical mass, you will have a great source of constant nutrition for your fish.


Disc Algae is found in aquariums with lots of light and calcium.  It is a green, hard type of algae usually found on the glass, although in a really well lit tank it can be found actually growing on plants.  Not many fish eat this algae, so you usually end up scraping it off the front sheets of glass with a single edge razor blade. 


Beard Algae is a short, all one length, algae that looks like a fur coat.  It comes in a few different colors like black, green/gray, and red.  It requires fast moving water, so it is often found around the outlet of filters, power heads, anywhere there is plenty of water flow.  A flat piece of slate covered with this algae looks incredible with water flowing over it.  Common Plecos seem to not have a taste for Beard Algae, but it is enjoyed by African cichlids and the Siamese algae eater (Crossocheilus Siamensis). 


Green Water Algae is a free-floating type of algae, which if left unchecked, will turn your aquarium into “pea soup”.  The most common occurrence of this algae is when somebody leaves their aquarium light on 24 hours a day, or when an outdoor pond is first set up.  These tiny one-celled algae are so small that they pass right through a regular filter cartridge.  Hobbyists raising their own Rotifers (Water Fleas) or Brine Shrimp use Green Water Algae as a prized food source.  Control of this algae is as simple as only leaving the light on 8-12 hours a day.  If you are in a hurry, a diatom filter (Magnum350 or Vortex) can filter down to 1 micron, thus easily capturing these tiny plants in about 3 hours.  In an outdoor pond, the only realistic method of control is to use an Ultraviolet Filter to kill these free-floating algae with radiation.



There are a few instances where you don’t want algae.  One would be the front glass of your aquarium.  This is where a Pleco or two comes in handy.  Plecos are lazy and would rather clean algae from the easy to clean glass surface than the rough surface of rocks.  This works out rather well for us, the aquarium keeper.  A point to keep in mind is that some Plecos are better than others as far as eating algae.  The Bushy Nose Plecos (Ancistrus sp.) are a family that does a great job.  The soon to be extinct Zebra Pleco favors rotting wood over algae, so it would be a poor choice for algae control.  In an aquarium filled with large, territorial cichlids, it’s hard to beat the Hypostomus Pleco as it can grow to almost 3 feet in length, and has an appetite for algae to match.  If you find the occasion where the Plecos have not kept up with their algae control duties, just wipe or scrape the front glass manually and maybe cut back on how much you are feeding the tank.  If those lazy Plecos are getting lots of fish food, they will slack off on the tank cleaning.


Another instance where algae could be a problem is if you were keeping a planted aquarium.  Although it would need another article in itself, a well planted aquarium will out compete algae for nutrients.  So, when starting a planted aquarium, the trick is to start big.  Having too few plants to start is an invitation for an algae take over.  Algae killing chemicals will harm most aquarium plants too (and your lawn if the pond is drained onto it).   Keep this in mind if you use the wastewater from your aquarium to water your houseplants.  In fact, the last thing the earth needs is more chemicals seeping into our waterways.


So, to sum it all up, algae is an important part of a natural aquarium.  Some algae are better than others as far as being a desirable part of your home aquarium.  Lighting amount and spectrum are both an important part of the algae equation. Many options can be used to control the growth of algae (fish, lighting, nutrients, UV, chemicals), with chemicals being the worst of the choices.  It may take some getting used to, but an aquarium filled with algae should be in your future as you advance in this great hobby.




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