Get Rid of Algae in Your Aquarium

Posted by on Jul 13, 2011 in All Categories, Problems and Worst Cases | 0 comments

Get Rid of Algae in Your Aquarium

A Quick Tutorial on Combating Algae in Freshwater Aquaria

I used to struggle with algae. At one point I had even considered to give up the hobby altogether.

Today, I see much clearer. I used to make some big mistakes. When it comes to fighting algae, there are some DOs and some DON’Ts. And there are helpers. I’ll talk about the useful creatures further down. But first, I want to talk about the water.

Alternanthera reineckii

Healthy plants are less likely to allow algae growth. (Alternanthera reineckii)

“An aquarium is a form of art, and the art is to create something, which will interpret nature not scientifically but in a poetic way.  The confines of the vessel are dissolved by perfection in numerous details.”

How Does Water Quality Relate to Algae Growth?

The simple answer is: A lot, but not always in ways you think.

Of course water quality is a determining factor in which and how many algae you encourage to grow in your aquarium. But what exactly is water quality? Every book you read on aquarium keeping will ram this point home: High nitrate and phosphate levels, along with other macro nutrients, will promote algae growth. But why do I read posts like this all the time:

“All my water values are OK, I have zero nitrate,
zero phosphate, 0.1mg/l iron, 25mg/l CO2 and lots
of plants. Yet there are <blue-green algae>.”

(Substitute the <blue-green algae> for any other type of algae.)

Nobody is surprised when no algae grow in polluted water but everybody is outraged when the opposite is the case.

I won’t get into the details of which algae prefer which particular environment and how they are different. Others have done this and a lot is known about different types of algae. Instead, I’ll give some insight on why there is algae growth and how to keep it in check.

Healthy Plants Will Outcompete Algae

First of all, it is wise to keep your water looked-after with controlled levels of macro-nutrients, including phosphorous and nitrogen. It is even a prerequisite to an algae-free aquarium. It is important to consider that your plants need these nutrients to grow and compete with the algae. This is something you have read somewhere as well, haven’t you? “Keep your plants healthy and well-fed so they can outgrow the algae”. But how can I keep my plants fertilized and not at the same time feed the algae?

Blyxa japonica

Even medium growers like Blyxa japonica can be kept totally algae-free.

So how can you change your fertilizing regime to overcome this apparent contradiction? It has been shown, that a good way to administer macro-nutrients is in bursts(*1); I recommend to do it two days before you change the water. Aquatic plants will soon absorb the nitrogen and phosphorus and you flush the rest out with the water. Algae need to grow to keep alive and their storage capacity is much lower than that of the plants. While they may benefit for a short period from the fertilizer, the plants will eventually prevail. Also, levels needed to support plant growth are very minimal. Tap water in some regions already contains 25mg/l, or more, of nitrate. This is a lot of nitrate. If you have such amounts of nitrate in your tap water, you do not need to add any extra nitrogen. Your best strategy is to adapt your fertilizing mixture to your tap water.

You need to understand also that, when algae die, they release the nutrients they have accumulated. That’s why you need to change the water regularly. If algae are not a problem, you can change about 1/4 once a week as a prevention. If algae are present, much more water needs to pass through your tank until an equilibrium is reached. Do not use so-called algicides! Chemical warfare will either kill your plants along with your algae or it won’t do anything at all!

Kaufmann gives a short instruction on how to cure an infestation with blue-green algae (Cyanobacteria). I am sure this can be adapted to fight other types of algae as well, should you need a fast remedy:

  1. Change 70% of the water
  2. Install an aerating pump with a diffusor
  3. Turn off all CO2
  4. Darken your tank by covering it with a blanket, cardboard etc.
  5. Only if small fry is present, feed every two days under dim light
  6. If infestation is severe, change 50% of the water again after three days
  7. after 6 to 7 days, return to normal lighting
  8. On the following two days, change 90% of the water on each day.

(Kaufmann states that if you forget or omit step 8, the whole exercise will be futile.)

Once you have returned to normal operation, keep micro-nutrients such as iron, potassium etc at an even level throughout. Administer these on a daily basis to replenish any deficiencies due to plant uptake.
This strategy obviously works best as a prevention measure and will ensure that your tank stays balanced and your plants healthy. Even algae infested tanks will eventually reach an equilibrium, if you follow this fertilizing regime.

You should also be aware that the number one fertilizer to plants is CO2. In high intensity, higher maintenance tanks with plenty of light, CO2 will soon become the limiting factor to plant growth and plants will start to break up CaCO3 (Calcium Carbonate) to get to the CO2. This is a costly process and in some plants, it will stunt growth. At the same time, algae will thrive because they are much more effective in utilizing CaCO3 as a source for CO2 due to their purely aquatic nature. Most aquarium plants however are submerged amphibious plants. Kaufmann (2010)(*2) states that algae benefit in another way from this: They can incorporate the CaO (lime), that is precipitated during CaCO3 breakup into their cell structure. This will render them unpalatable to algae eating foragers.

Rotala macrandra

Oxygen bubbles in Rotala macrandra are evidence of high CO2 uptake

Don’t get me wrong: You can have beautiful aquaria without CO2 but we are talking about a totally different type of tank here. Low-intensity tanks require less of everything and different types of plants are kept in them.

Algae Will Create Their Own Favourable Environment

Healthy and vigorous plants will outcompete alge because they bind free nutrients and create an environment which is favourable to their growth. The same is true for algae. Once you have them, it is hard to get rid of them because they create their own environment. By the way: One of the reasons why nitrate or phosphate levels are often apparently very low in aquaria but there’s an abundance of algae is hardly surprising. The nutrients are locked up inside of the algae. Thus, radical water changes are recommended when you run a blackout cure as recommended above. When algae decay, their proteins are metabolized into anorganic nitrogen compounds.

Some of the algae can be siphoned or netted off but with most algae, you’ll have a hard time to get rid of them, once they have taken over. You can help your plants by removing as many algae as possible, though: Start by keeping your aquarium sides clean. It is the easiest and also a very effective measure in preventing an algae-friendly environment. And it will encourage you to see the beauty in your aquascape, beyond the algae. Read on for further measures.

Useful Creatures: Algae Eating Fish And Invertebrates

In my experience, even with a rigorous regime of water changes, perfect fertilization and good lighting, you will still sometimes have a few algae. Not many but a few. If you’re a perfectionist, you will strive for the same look you see in competitions, where completely algae-free plants show glossy leaves without a trace of anything that doesn’t belong there. Ultimately, an aquarium is a form of art, and the art is to create something which will interpret nature not scientifically but in a poetic way:  The confines of the vessel are dissolved by perfect detail.

If you look at most award-winning planted tanks, you can’t help noticing that there are always some creatures in there that feed on algae. These little helpers are a great support in creating an aquarium which is completely devoid of algae. You have a choice of algae eaters, each with their own characteristics. I’ll introduce the most important ones of them here with a short description of what to look for in each helper.

The “Amano Shrimp”, Caridina multidentata

Caridina multidentata

Caridina multidentata is an excellent algae eater

Perhaps one of the best-known algae-eaters, the Amano shrimp will get rid of a broad range of algae, including most green algae. These invertebrates are restless eaters and will munch away on algae, uneaten fish food and the occasional undiscovered deceased fish. I would never start a new tank without them. Make sure to get numbers right though as too many of these shrimps will eventually turn to your plants once algae populations have been eradicated. On the other hand, if you don’t have enough at hand, their grazing power will not suffice to get rid of the algae. Another fine example to illustrate the  rule that you need a good sense of balance as an aquarist. Rule of thumb is about one shrimp per 7 litres of water but there are exceptions (See this post).

Siamese Algae-Eaters

There are different types of Siamese Algae Eaters and not all of them are suited for the task. (Check out this excellent article on algae eating cyprinids). I have had a relatively uncommon type, Crossocheilus reticulatus, for three years now and it has to be said that these fish are perhaps the best weapon against filamentous red algae. Red algae are among the most tenacious of algae. They appear in tufts of very fine, black hairs on the edges of slow growing plant leaves and will eventually cover every inch of decoration. C. reticulatus will soon eat both the aforementioned type as well as the stag-horn type which is coarser, more branched and slightly slimy to the touch. Like the former type, it is also black and looks like miniature stag horns. The reticulatus type of algae eater is a bit plain to look at but easily recognized by the black dot on the base of the tail fin.

Crossocheilus reticulatus

This piece of driftwood has been cleaned of algae by C. reticulatus

Another, more common type is the Siamese Algae Eater. I have only had three of these for a few weeks in a tank where some red algae have started to develop and it is too early to say how they will do against these as they are still very small. I’ll keep updates coming in as soon as there is anything worth sharing.

Crossocheilus siamensis

Crossocheilus siamensis

 Otos (Otocinclus affinis)

These small catfish are  great to keep broadleaved plants in shape. I have never seen an Otocinclus destroy any of the leaves it feeds on – on the contrary: Plants seem to like this little creature and become all nice and glossy once these fish are introduced into the tank. Unfortunately, Otocinclus do not like to travel and you are likely to lose some during the first couple of weeks after introducing them to your tank.

Otocinclus affinis

Otocinclus affinis is a gentle cleaner

If you have a nano aquarium or a very small tank you should definitely go for the Caridina or the Otocinclus as the Cyprinids will simply grow too large to fit into anything unter 200l (53 gal.).


Eliminating algae involves getting many things “just right”, which is what makes this difficult: it is a balancing act. Too much of anything is often damaging but too little is not beneficial either. It has to be said that an aquarium is a living thing and cannot be “hooked up” like a computer. A constant watchful eye will help you get a feel for the right measures. Don’t let setbacks frustrate you: Once you have mastered the art of the algae free aquarium, you will enjoy this great hobby immensely.

1: Hans-Georg Kramer, Pflanzenaquaristik à la Kramer
2: Bernd Kaufmann, Algen-Fibel Aquarium

All images copyright by Stephan Mönninghoff

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