Algae in Aquarium – An Introduction to Algae

What is Algae?


Algae is an informal term for a wide range of plant-like organisms. These organisms can be either unicellular (Chlorella, diatoms, etc.) or multi-cellular (Giant kelp, seaweed, etc.). Some types in the aquarium are acceptable and beneficial at low amounts as they consume excess nutrients and produce oxygen. Also, they provide food to some fish. But overpopulation disturbs the ecological balance in the aquarium and is harmful to fish and plants. Also, it will cause a bad view in case it overgrows and covers many surfaces.


Like plants, algae produce their food by photosynthesis for which they need water, light, and nutrients. The most common causes are:

Improper Lighting

• An aquarium receiving direct sunlight, even for few hours per day.
• Excessive lighting.
• The intensity of aquarium bulbs reduces in time. Some types like brown algae, grow due to the low-intensity lighting from older bulbs.

High Nutrient Levels

• Overfeeding the fish is one of the most common causes of the overgrowth of algae. Leftover foods and fish excreta are rich in nitrogen compounds and phosphates, the nutrients which are required by plants and algae to grow.
• Tap water is high in minerals and nutrients, and using it directly without filtering can be also a problem.
• Using excessive fertilizers in the early stages of aquarium setups will also surely cause algae blooms.

Algae Prevention

The best way to deal with algae is to be proactive and take preventative measures before it takes over. Not allowing algae to grow in the first place is easier. Also, it will be less stressful for the fish and yourself as well.

The below steps can be helpful to ensure an algae-free aquarium;


Have Proper Lighting

Do not place your aquarium under direct sunlight. If it is a planted aquarium do not leave lights on for more than 10-12 hours per day. Lighting periods can be set as 3 hours on and 1 hour off to have more efficient plant growth and decrease algae growth. For aquariums without plants, the lights should be on for no more than 8 hours per day. Changing the aquarium bulbs once every 6-10 months will also help. Since the wavelength changes and becomes proper for algae growth in time, changing the light bulbs is a good practice for prevention. Due to this creates extra costs for every 6-10 months LED lighting can be an alternative option for long-term uses.

Avoid Overfeeding

If the fish food is left uneaten by fish within the first two, three minutes, it usually means you are feeding the fish excessively. Learn your fish’s requirements and feed only as much as they need. Afterward, remove any leftovers because they increase the nutrient levels in the water. Even the fish consume all of the food, if you are overfeeding, the fish wastes will release nitrogen and phosphate. In case the filtration is not effective enough to overcome the organic wastes produced, it will probably cause algae growth.

Water Changes

In nature, the nutrients building up in the water over time are diluted by rain or flows by water. You should substitute this in the aquarium by making partial water changes (up to 50%) every week. This will also help to neutralize the poisoning effects of nutrients dissolved in the water. For example, high concentrations of Nitrogen compounds will cause gill irritation that will cause fish deaths.

Testing Water

Testing water, which you are adding to the aquarium for phosphates and nitrates will provide an opinion to notice if it may cause an algal bloom or not. For the tap water, test if in either of those nutrient levels are high, you need to change the water source or establish a Reverse Osmosis unit to filter the water before setup or water changes.

Adding Plants

Plants are natural competitors to algae as they require the same resources to thrive. A well-planted and cycled tank usually has very low amounts of nitrogen and phosphorous, and hence very little algae. For the new setups, fast-growing plants such as elodea sp. is a good choice since they consume the nutrients very fast and help to prevent any possible issue before it occurs.

Floating plants are also excellent choices due to that they diffuse less light into the aquarium. In addition, they are taking up most of the available nutrients.



Having algae-eating species in your aquarium is also an effective solution. Nerite Snails are one of the best algae eaters. They will scrape the hard green algae off the aquarium walls and substrate. Some fish species like Otocinclus or Ancistrus, suckermouth loaches, Chinese algae eater (Gyrinocheilus aymonieri), and Mollies (Poecilia sphenops) are also well known as an alternative. Amano shrimp (Caridina multidentata) and cherry shrimp (not as much Amano shrimp) are also effective.

Note: Amano shrimp is the best on eating many types of algae and very famous in the worldwide aquarium community.

Identification and Cure

You should monitor the aquarium regularly for signs of any algae growth. If you notice it appears, you should identify its type and determine the cause. Swift action to remove the algae and remedying the cause prevents it from taking over your aquarium. The most possible cause in the aquarium is the imbalanced nutrient levels. So, balancing the nutrient levels will be the best to prevent it before it starts to grow and spread. A well-established aquarium with proper levels of lighting, nutrients, and CO2 is necessary to prevent algae growth. Below some optimum levels are given for reference.

Optimal Levels of CO2 and Other Compounds:

• Carbon-di-oxide (CO2): 20-30 mg/liter
• Magnesium (Mg): 0-10 mg/liter
• Nitrate (NO2): 10-25 mg/liter
• Phosphate (PO4): 0.1-1 mg/liter
• Potassium (K): 5-10 mg/liter

Having the perfect water conditions does not mean it will completely prevent any algal growth. However, it will help you to control their amount and prevent them from taking over your aquarium.

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