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Controlling Algae Growth

Controlling Algae Growth

Algae growth is an incredibly common problem with freshwater tanks. Read more to learn why it happens and how to control it.
If you have ever seen an aquarium covered in slimy or fuzzy green growths, you have seen algae. Algae is one of the most prevalent problems encountered in the aquarium hobby. Not only is algae overgrowth frustrating and difficult to deal with, but it can also destroy the appearance of your aquarium and interfere with the health of your fish and live plants. It is important to realize that algae growth can be controlled, however, if you know what to do. This article will discuss not only the causes of excess algae growth, but also some tips for how you can minimize it.
Before we discuss how to eradicate algae, it should be mentioned that some algae growth is perfectly normal in a healthy aquarium. You will never be able to completely stop algae from growing and as long as it doesn’t become excessive, it does not harm your fish. Simply wipe off algae from places such as the front glass and it should take a week or two before you need to wipe it off again. If it is growing back within a couple of days, however, you should read the rest of this article and learn how to properly control your algae.
Causes of Algae Growth

If you want to eradicate algae from your aquarium, it is vital that you understand why it grows in the first place. Your only hope in preventing the regrowth of algae is to remedy the problems that caused the overgrowth in the first place. Algae have certain needs that must be met in order to survive and flourish. Algae require light, nutrients from the water, and a lack of predators. Without these key components, algae will have a difficult time taking off in your tank and, therefore, it is these areas that you should address.  

Algae, White Island by Kenneth Allen via Wikimedia Commons


Light is a major factor in algae growth because these organisms engage in the process of photosynthesis in order to grow and reproduce. The simple fact is that many people keep their lights on for too long – an excess of light will provide an abundance of energy for algae to grow. The lights in your tank should be on no longer than 8-10 hours per day (if you are growing live plants then the recommended length of time is closer to 12 hours, but the addition of plants should offset the additional hours of light more on this later). Timers are very helpful in that they ensure your tank is receiving the correct hours of lights per day.

To avoid giving your tank too much light, you should also make an effort to keep your tank out of direct sunlight. Not only will direct sunlight increase the lighting in your tank, but it can overheat the tank as well and make it an even more suitable environment for algae to grow. If you place a tank in a window where the sun hits it for several hours a day, you are asking for trouble.

Not only can too much light cause you problems, but too little light can also lead to excessive algae (in particular, brown algae). Therefore, it is not generally a good idea to simply stop turning your light on to get rid of the algae. Instead, you should shoot for the 8-10 hour range. Changing your light bulbs every 6 to 12 months will also help to control algae growth. Though the light bulbs may still produce light, most bulbs lost their intensity after this amount of time which can lead to an increase in algae growth.

Not only is the amount of light important in the growth of algae, but the type of lights you have also dictate its propagation. For instance, actinic lights began in the salt water realm, but are seeing increased use in fresh water systems. However, actinic bulbs can lead to algae outbreaks. There are numerous examples of people who switched out their actinic or 50/50 bulbs and had their algae decrease rapidly. Bulbs that have temperatures of 6500 K or below seem to be the best in terms of not promoting algae outbreaks. If you have tried reducing your lighting period and still are having algae problems, investigate the temperature of your bulbs and see if that is the root cause.


Algae require nutrients in the water in order to grow -- these nutrients are usually in the form of nitrates or phosphates. It is, therefore, helpful to test for these compounds if you are having algae problems. If your tests show high levels, first test your tap water to see if it is naturally high in either of these compounds. If it is, you may have to purchase distilled water or treat your tap water (with reverse osmosis, for instance).

If your tap water is not naturally high in nitrates or phosphates, then your tank may be overcrowded or you may be overfeeding. Your fish should generally be fed 2-3 times a day with each feeding lasting a couple of minutes. If you consistently overfeed, the left-over food will make the nitrates spike. It is vital that you cut down on your feeding if your nitrates become too high (greater than 20 ppm). Frequent water changes will also help reduce the nitrate concentration as will vacuuming the substrate. A thorough vacuuming is often a key missing element in fish maintenance, but it is very useful in getting any uneaten food out of the substrate and removing fish waste.

Because an abundance of nutrients will lead to algae overgrowth, another way to rob the algae of nutrients is to provide competitors. If you heavily plant live plants in your aquarium, they will use up some of the nutrients that algae needs in order to grow. In the process, they are ensuring that the algae will not have enough to eat. Keep in mind, however, that adding live plants may change the lighting requirements in your tank as well – plants need light in order to grow, so don’t try to add live plants without also increasing the lighting in your tank.

One of the most commonly recommended algae eaters is the common plecostomus (pleco). Unfortunately, this recommendation is misguided and can lead to more problems in the tank. In general, a common pleco is not a good solution to getting rid of algae because it will eat some kinds of algae when it is young, but stops eating algae all together when it reaches a length of around 5-6. From this length on, not only does it not eat your algae, but it contributes greatly to the load on your tank as it produces a great deal of waste and eventually becomes a very large fish that may become aggressive as well.

Macrotocinclus Affinis Looking for Algae by Cisamarc via Wikimedia Commons

Stocking predators can be a very effective means of eradicating algae in your tank. However, care needs to be taken when choosing which fish to purchase. Many of the algae-eaters will only eat certain kinds of algae, thus you need to find out which kind of algae you have first and then you can select a predator to eat it. You also need to see how long the predator will eat algae (see the discussion on the common pleco above for an example of this). Some of the more effective algae-eaters include otos (tend to be the best option for smaller tanks), bristlenose plecos, American flagfish, and rubberlip plecos. Be sure to research these fish before you purchase them to make sure they are suitable for your specific aquarium and eat the right kind of algae. 

Refer to the list below for recommended species of algae eater:

Siamese Algae Eater – brush algae, thread algae, flatworms
Amano Shrimp – all types of algae, plant detritus, leftover food
Otocinclus Catfish – young algae growths, brown algae
Malaysian Trumpet Snail – all types of algae, plant detritus, leftover food
Ramshorn Snail – all types of algae, plant detritus, leftover food
Bristlenose Pleco – various types of algae
Black Molly – beard algae, other algae growths
Butterfly Goodeid – red algae, green algae, beard algae
Florida Flag Fish – hair algae, beard algae
Rosie Barbs – hair algae
Flying Fox – hair algae, brush algae, slime algae


Minor algae growth is inevitable in your aquarium. In fact, the look of a tank is often enhanced by the subtle growth on rocks or the back glass. Problems occur, however, when the algae starts to take over your tank. If you encounter this problem, read over the suggestions in this article. Most algae problems can be solved by reducing the hours of light, changing the temperature of the light, reducing the amount of food, reducing the number of fish, adding live plants, or adding predators. There are some types of algae blooms where more extreme methods needs to be used, but the recommendations in the article will help in the control of most algae.

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