Aquarium & Tropical Fish Site

Freshwater Algae Types: An Illustrated Guide

 Age of Aquariums > Aquarium Articles


Almost every aquarist will at some point face an algae outbreak in a tank, and as we have learned from this previous article on the site, algae control is all nutrient control. But one thing has to be clear: it is not the same when it comes to controlling algae in planted and non-planted tanks!

In a non-planted aquarium,
nitrate and phosphate levels can easily go high, and result in an algae outbreak. Overfeeding and overstocking is the most common reason for water quality going bad like that. Weekly water changes are the best solution in reducing these nutrients. The ammonia (NH3), ammonium (NH4) and nitrite (NO2) levels should be at 0 ppm. Nitrate (NO3) levels should ideally be kept below 10 ppm (nitrate levels over 40 ppm can be dangerous for some fish and invertebrates). Phosphate (PO4) levels should be kept below 0.5 ppm. Lights should be on no more then 10 hours per day. Note that most algae favours strong lights, so placing the aquarium away from the window is a good idea. Direct sunlight will almost certainly cause an algae outbreak. An algae eating army will help a lot in combating algae.

In a planted aquarium,
the situation is more complex because there are not just fish to consider, but also live plants. It is true that plants will uptake the ammonia/nitrate/phosphate and help keep the water chemistry in good quality. But even so you can suddenly experience the worst algae outbreak in a planted tank, and you will ask "but how is this possible?!"

Let's start answering with the fact that plants and algae need the same nutrients to thrive. Imbalance between lights, CO2, macro- and micro-nutrientes are the main causes that lead to algae growth, because when plants have all those elements balanced they are much more efficient at uptaking nutrients from water than the algae. Fast growing stem plants are very famous for keeping algae at bay for their ability to uptake nutrients in no time. But when, for example, just one of these elements is reduced, plants will slow down their metabolism and will leave nutrients available, sometimes even start leaking nutrients back into the water. Of course the plant will show symptoms like yellow leaves and pin holes in leaves, etc. It is not enough to add a few fast growing plants to fight algae, without providing the right nutrient balance for them to thrive. Only happy plants will lead to a balanced ecosystem. Since algae are nutrient scavengers and much simpler life forms than plants, they will take advantage in unbalanced systems. So, all we need to do is to make sure our plants have the right amount of lighting, CO2, macro- and micro-nutrients. The fertilising regime depends on how strong the aquarium lights are:

Low light tanks
have about 0.3 - 0.4 W/L (Watts per liter) of normal fluorescent lighting. CO2 can be added via DIY Yeast Reactor, that is inexpensive. Fertilisers like Tropica Master Grow are very good for dosing trace elements (micronutrients) like Fe, Mg, Zn, B, S, Mn, Cu, Mo and K. Homemade fertilizer mix (Poor Mans Dosing Drops, PMDD) is a very good solution for dosing macronutrients (N-P-K) and others. It is made out of KNO3, KH2PO4 and NutriSI mikro. NOTE; Because Iron (Fe) is the most important trace element, the tank substrate should have fair amount of Iron. Liquid iron will, if overdosed, favour hair algae. It can be added through ground Iron-rich fertilisers and through substrates like Laterite and Flourite. Low light set-ups that are injected with a fair amount of CO2 through DIY Yeast Reactor (1 bottle per 100 liters) should be fertilised at least once a week. I fertilise with PMDD and Tropica Master Grow. Stem plants, in this kind of set-up, will normally need to be pruned every few weeks. It is usually recommendable to perform 50% water change per week. This way we limit nutrient build-up, and after that the nutrients should be re-dosed. A good fertilising regime is to break the nutrients dosing every 2-3 days. When dosing nutrients only once a week, plants may have excess nutrients in the beginning and lack nutrients in the second part of the week, causing more variable, unbalanced conditions that favour algae.

You will find that many aquarists establish low light, low tech tanks and change water approximately every 3-4 months (low maintenance). To successfully run low tech planted tanks it is very important to have nutrient rich substrate. Some use ground peat, others clay or Laterite/Fluorite, and some mix together different types of substrates. The important thing is to cover nutrient rich substrate with approximately 4-5 cm of fine gravel, which will keep the water clean and nutrients away from algae. Liquid fertiliser should be added every month, half of the recommended dose and if plants show deficiencies, add the recommended measure. Low tech tanks are normally not injected with CO2, so the filter outlet should not disturb the water surface too much (white water, splashes, etc). In low tech tanks, plants will grow slow and will not need much pruning.

High light tanks
have 0.7 W/L or higher of lighting, and therefore need equally higher CO2 and nutrient levels to keep the correct balance for plants to grow fast enough and out-compete algae. A pressurized CO2 system becomes the best option and one should be ready to invest in it to have an algae free aquarium with lush plants. You may need double or triple the amount of fertilizing as in low light tanks. In high light set-ups CO2 should be monitored carefully and maintained at aroung 30 ppm. In both aquarium types (low and high light) the nitrate levels should be maintained at 10-15 ppm and phosphates at 0.5-1 ppm. To repeat one thing though, because it is 95% algae issue related; higher levels of CO2 (30 ppm) seem to keep algae at bay. Of course, algae eaters like SAE, Otos and Amano shrimp are more than a welcome addition. Snails like Malaysian Trumpet will help aerate the gravel. Trimming plants will do good since it will encourage new plant growth and stop older leaves from decaying and polluting the water. And remember, limiting nutrients is the right thing to do in non-planted tanks, but very wrong in planted tanks as in question. In high light planted tanks one should do weekly 50% water change, and among other options use the Estimative Index method for dosing nutrient.

NOTE; there are many articles on the net preaching that reducing nitrates and phosphates will help keeping algae low! In non-planted tanks yes, but in planted tanks NO! Plants need more nutrients than algae to thrive, so do not reduce nutrients, dose them!

Now that we know how to prevent algae in general, let's ID the most common algae types in freshwater aquariums and discuss specific causes and combat techniques:

  • Brown Algae (diatoms)
    are more likely to appear in low-light aquariums and new setups, where nitrogen (N) is low and phosphate (P) level is high, with excess silicate (SiO2). It's been known that strong lights make this algae go away, but they might still be seen on lower, shadowed, plant leaves (Bacopa australis, Cardamine lyrata). It can also be found on aquarium glass, gravel and decoration. It can be easily removed manually, since it has a soft/slimy structure. Siamese Algae Eaters, Otos (this catfish relishes this type of algae) and Snails can easily keep this algae in low numbers. Healthy plants can prevent this algae from over taking the tank.
    Photo credit: Dusko Bojic
    Note: the macro photo represents one of the many brown patches form the first photo. The Brown diatoms are rectangular shaped. Brown Algae diatoms Brown Algae diatoms
  • Green water (algae bloom)
    This is the most common problem if the cloudy situation extends beyond 10-14 days. Note that "green water" (GW) is not always green in appearance! Since GW is the most common problem and the most difficult to solve the answer needs to reflect several options. The situation that causes GW is usually a combination of high nitrates, phosphates, and mixed in some ammonia/ammonium. Substrate disturbance is usually the culprit. What happens is the algae (GW form) will flourish off of the ammonia/ammonium and phosphate, remembering that algae can consume phosphate easier than plants because of their thin cell walls, the algae uses up the ammonia/ammonium and phosphate, but it doesn't go away...because algae can quickly switch which nutrient it moves to nitrates. So you can see why water changes will not rid a tank of GW. Nutrients can be reduced very low in GW and fairly quickly by the GW algaes, but they can scavenge other nutrients...iron and trace elements. So, it's very common for the GW to solve the situation that causes it to begin with, but that won't eliminate the GW, for the reasons I've alluded to. Five methods exist to eliminate GW. Blackout, Diatom Filtering, UV Sterilization, Live Daphnia, and Chemical algaecides/flocculents. The first four cause no harm to fish, the fifth one does.

    Green water algae bloom Method No. 1 - Blackout
    The blackout method consists of covering the tank for 4 days, so no light whatsoever is allowed into the tank during this time. Cover the tank completely with blankets or black plastic trash bags. Be prepared, killing the algae will result in dead decaying algae that will decompose and pollute the water. Water changes are needed at the beginning and end of the blackout time and ammonia should be monitored also.

    Method No. 2 - Diatom Filtering
    Diatom filters can sometimes be rented from your LFS. This is my preferred method. Personally, I use my Magnum 350 w/Micron Cartridge coated with diatom powder. Diatom filtering removes the algae and doesn't allow it to decay in the tank. You do have to check the filter often, if you have a really bad case of GW the filter can clog pretty quick. Just clean it and start it up again. Crystal clear water usually takes from a few minutes to a couple of hours.

    Method No. 3 - UV Sterilization
    UV Sterilizers will kill free floating algae. They also kill free floating parasites and bacteria. They also can be problematic for extended use in a planted tank, as they will cause the “breakdown” of some important nutrients. They are expensive and don't remove the decaying material from the tank, if you can afford to keep one they are handy to have around, though not as useful IMO as a diatom filter.

    Method No. 4 - Live Daphnia
    Adding live daphnia to your tank. This can be a bit tricky. First you need to ensure that you are not adding other "pests" along with the daphnia. Second, unless you can separate the daphnia from the fish, the fish will likely consume the daphnia before the daphnia can consume all the green water.

    Method No. 5 - Chemical algaecides/flocculents
    I hate the last way, the flocculents stick to the gills of fish. Although it won't actually kill them, it does compromise their gill function for quite a while, leaving them open for other maladies.

    (Written by Steve Hampton)
    Photo credit: Luca
  • Green Spot Algae
    enjoys plenty of light. It forms green spots on aquarium glass and slow growing plants that are exposed to strong light. This algae will appear if CO2 and Phosphate (PO4) levels are low. Since it is very hard, algae eaters can't do much in eliminating this algae. Neritina snails are the only algae eaters I know that will graze on Green Spot Algae. It can be scraped manually off the glass with a razor blade or plastic card. In the case of an acrylic aquarium use plastic only. This algae is considered normal in small amounts. To prevent this algae, do weekly water changes, do not overfeed nor over-stock. In planted tanks keep slow growing plants in places where they will get less light (low light set-ups should not suffer from this algae in large extents) and keep Phosphate levels between 0.3-0.5ppm and CO2 levels 30 ppm.
    Photo credit: Dusko Bojic
    Note: The Green Spot algae in the Macro photo are no bigger than 1/8mm. Green Spot Algae Green Spot Algae
  • Blue-Green Algae
    even though it's commonly called blue-green algae (BGA), it's not classified anymore as one. This "algae" is actually cyanobacteria, a form of life that has both animal and plant characteristics. It forms slimy, blue-green, sheets that will cover everything in a short time and give off a strong, characteristic scent. If left to over-run the tank, cyanobacteria may kill plants and even fish. It doesn't stick and can be easily removed manually, but will return quickly if the underlying water quality issue is not fixed. It can be treated with Erythromycin and other antibiotics, but this method should be done carefully since it might affect the nitrifying bacteria in the gravel and filter, and improper use of antibiotics always brings the risk of developing a more resistant strain. When the BGA gets killed by the algaecide it will start to rot and through that process it will reduce Oxygen levels in the tank. Since the nitrifying bacteria needs O2 to transfer ammonia/nitrites into nitrates the nitrifying process will slow down. If algaecide is used, make sure to test the ammonia/nitrite levels. Remove all the visible algae to prevent it from rotting in side the tank.

    Some aquarists use the black-out method previously described, where black bags are wrapped around the tank for 4 days and held in complete darkness. It is advisable to raise NO3 levels to 10-20 ppm before starting the black-out period. Manually remove as much BGA as you can before the blackout, and dead matter after the blackout.Egeria densa (Elodea) and Ceratophyllum demersum are good plants to have in a tank, since these plants are known to secrete natural antibiotic substances that can help prevent BGA. Establishing lots of healthy, fast-growing plants from the day you start the tank, dosing the nitrate levels to maintain 10-20 ppm, and vacuuming the gravel to keep the tank free of decaying matter is the best way to prevent this "algae". BGA can be found in aquariums with very low nitrates because it can fix atmospheric nitrogen. BGA seems not to like high CO2 levels and stronger water currents.
    Photo credit: Dusko Bojic
    Note: The second photo is photographed macro. The BGA are tiny threads that will in short time form a slime sheet. Blue-Green Algae Blue-Green Algae
  • Green-slimy, water surface film
    This is a protein film. I don't know what type of algae grows in it. Taking a sample under the microscope would probably give some answers. The best way in combating slimy surface film is to improve surface agitation. Filter should be rinsed every week, so the water can flow better through it. To prevent it, use Active Carbon every 2-3 month for 3 weeks and Zeolite to get rid of the organics that tend to build up in aquariums, especially the older ones. 50% weekly water changes will help a lot in reducing organics. The film can be removed with paper towels. Black Mollies will eat this sort of algae. The aquarium shown in the photos are of a low light tank. Green-slimy, water surface film Green-slimy, water surface film
  • Cladophora algae
    Cladophora is a branching, green filamentous alga, that forms a moss like structure. This algae doesn't appear to be slimy. Threads are very strong and very thin. It grows on rocks and submersed wood exposed to direct light, and in extreme cases will grow on plants also. Usually it tends to stay on one spot, which makes it easy to remove. Comb it and dose more CO2. In a case where Cladophora takes over the grassy plants, mow the plants like the lawn. No algae eater is known to eat this kind of algae.
    Photo credit: Dusko Bojic. Cladophora algae Cladophora algae
  • Thread Algae

  • Thread Algae
    grows on leaf edges as individual, up to 30 cm long threads. It is easily removed by twirling a tooth-brush around it. Excess iron is a possible reason. It is better to use substrate iron fertilisers, since this algae uptakes the iron from the water. Healthy plants will out-compete this algae. Algae eaters like SAE and Caridina japonica will consume it. Thread algae is very likely to appear together with the Hair algae.
    Photo credit: Irons
  • Hair Algae

  • Hair Algae
    forms around the base of slower growing plants, on gravel and bog-wood. It has green-gray color. It grows up to 4 cm, sometimes more. It is easy to remove this algae by twirling a tooth-brush around it. Most aquarists find this algae very welcome as a good food supplement for their fish. Most omnivorous fish like Angels or Barbs will supplement their diet with hair algae if not over-fed. In stronger water currents this algae forms matted clumps, as well as that, stronger water current will disturb their growth. All algae eaters will be more than happy to look after the Hair algae for you.
    Photo credit: Dusko Bojic
  • Staghorn Algae
    grows in long individual strands that form a few branches. It will grow close to the light source on equipment and plants. Strands can be pulled off the surface or in very bad cases the whole leaf should be discarded. Higher ammonia/ammonium levels (from overstocking or substrate disturbance) and low CO2 levels will favour this algae. It's been known that the Siamese Algae Eater will keep this algae in check. Nutrient control and healthy growing plants will limit Staghorn algae.
    Photo credit: Dusko Bojic Staghorn Algae Staghorn Algae
  • Beard Algae

  • Beard Algae
    can actually be an attractive addition to an aquarium on big pieces of stone and/or bogwood. It forms a thick green carpet over the surface closer to the light source. It is very soft and slippery but it is impossible to be removed mechanically. It can also be seen on slow growing plant leaves. It grows approximately 3 cm and the growth is rapid. The best way to control this algae is with the Siamese Algae Eater. Plecos are known to eat this algae, as well as Rosy barbs and Red Tailed Shark, but you should first check whether these fish are compatible with your other fish and with your tank size. Keeping lights for more than 12 hours a day will trigger this algae, as well as unbalanced nutrients. It will show up in planted tanks with low CO2 and NO3 levels. This algae can be found in low and high pH waters. Beard Algae is very common in non-planted aquariums.
    Photo credit: Dusko Bojic
  • Fuzz Algae

  • Fuzz Algae
    grow on leaves and plant stems not necessarily exposed to strong lights. The affected plants are probably suffering deficiency problems and are leaking nutrients back into the water. This algae is considered normal in small quantities. Aquariums with fish such as Siamese Algae Eater, Otos, Amano shrimp, Bristlenose pleco or Mollies will not suffer from this algae. Balanced nutrients will give head start against the algae.
    Photo credit: Gianmarco Bertaccini
  • Brush/Red Algae

  • Brush/Red Algae (Black-brush algae)
    has been known to thrive in both acidic and alkaline waters. In hard waters it will form lime tissue (from biogenic decalcification) which makes it harder to be eaten by the only algae eater known to eat this type of algae, the Siamese Algae Eater (SAE). Biogenic decalcification can be prevented by adding CO2. Healthy fast growing plants will out-compete this feathery-black algae that tends to grow on slow growing plant leaves. When buying new plants, before planting, it's good to soak them into a weak household bleach solution for two minutes. 1 part of plain bleach (don't use bleach that has lemon, orange or any kind of scent) to 20 parts of water. Do not forget to rinse the plants well with clean water before adding them into the aquarium. The only perfect way to combat Brush algae is planting lots of healthy fast growing plants, introducing a few SAE, maintaining CO2 at 30 ppm, nitrates at 15 ppm and phosphates at 0.5 ppm. Leaves that are badly overtaken should be discarded.
    Photo credit: Dusko Bojic
  • Green Dust Algae

  • Green Dust Algae
    are actually zoospores and are commonly found on aquarium glass. They form a dusty looking, green patchy film and in severe cases can cover the whole aquarium glass. It's not known what actually causes this algae. Intense light is favored by GDA. Scraping it off the glass will not help remove this algae since it stays in the water and will float for 30-90 minutes before attaching it self again to the glass. For some reason those zoospores seem to avoid plants, rocks and wood and always go for the glass. Limiting nutrients will not help fighting this algae, but rather cause problems in planted tanks where plants will be exposed to nutrient deficiency and that condition will just favour other algae types. The best known solution for getting rid of GDA has been proposed by Tom Barr. He claims that this algae should be left alone to grow, without wiping the glass for about 10-20 days. After this period GDA will start forming a thick patchy film that will start falling off the glass. When this starts happening it is good to remove this algae out of the tank. This method should keep this algae at bay.
    Photo credit: Dusko Bojic

  • Reader Comments

     Submit a Comment 

    Got some experience to share for this page? No registration necessary to contribute! Your privacy is respected: your e-mail is published only if you wish so. All submissions are reviewed before addition. Write based on your personal experiences, with no abbreviations, no chat lingo, and using proper punctuation and capitalization. Ready? Then send your comments!

    oF <=> oC in <=> cm G <=> L