How to Prevent Algae Growth in a Freshwater Aquarium

Co-authored by Aaron Bernard and Jessica Gibson

Last Updated: August 25, 2021 References

Setting up a freshwater aquarium takes time and skill so you want to show it off! Sometimes, however, an imbalance in the tank's water can cause algae to grow. If you want to prevent unsightly algae from hiding your beautiful tank, read through our list of tips. These can help fight common freshwater algae like green, brown, and blue-green algae.

Method 1

Method 1 of 9:
Reduce the amount of light your tank gets.

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Set a timer for tank lights so your fish get 6 to 10 hours of light a day. If your tank's lights are on all day, it's probably too much. All this light helps algae photosynthesize and create energy for more growth. If your tank has live plants, set the lights to be on for 10 hours a day. If you don't have plants or you have plastic ones, set the timer for 6 to 8 hours.^{[1]
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- Freshwater aquariums don't have strict lighting needs like saltwater tanks do and fish don't have specific lighting needs based on species, so anywhere from 6 to 10 hours of light a day is fine.
- This is especially important if your tank is near a window and you can't move to another room.
- Don't have a tank timer? No problem—write down a daily schedule for when you turn the lights on and off. To make it easier to follow, set reminders on your phone.
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Method 2

Method 2 of 9:
Lower the water temperature.

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Warm water and sunlight encourage algae to thrive in your tank. If you don't already have a tank thermometer, put one into the water so you can see if the water is warmer than it needs to be. Most fish like the temperature between 76 and 80 °F (24 and 27 °C). If it's warmer than that, turn down your tank heater.^{[2]
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- Cool water slows down algae growth so keep an eye on the temperature.

Method 3

Method 3 of 9:
Keep the water in the tank moving.

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Add a water pump to prevent debris from building up in your tank. If water's not circulating in your aquarium, debris can settle in spots and algae will start to grow. Putting even a simple water pump into the tank can keep the water moving so filters can remove debris and keep the tank clean.^{[3]
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- Good water circulation also keeps your fish healthier since they'll get more oxygen out of the water.
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Method 4

Method 4 of 9:
Replace plastic plants with live ones.

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Plants like mosquito fern remove the nutrients that algae need to grow. Water sprite or foxtail plants are also great choices for your freshwater aquarium. All of these plants remove nitrates and phosphorus that algae needs in order to grow. Plus, they make your tank look beautiful!^{[4]
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- Algae won't grow on the live plants the way they do on plastic ones, so there's less cleanup.

Method 5

Method 5 of 9:
Cut back on feeding your fish.

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Switch to feeding your fish several small meals instead of big ones. It's best to have your fish eat everything you sprinkle in the tank within a few minutes. If you're feeding them too much, that food starts to decay in the water, which feeds algae.^{[5]
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- You might find that you only need to feed your fish once or twice a day. If your fish don't eat that often, try feeding them every other day.
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Method 6

Method 6 of 9:
Buy fish and shrimp that eat algae.

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Fish like cory catfish, oto cats, and pleco fish eat algae and tank debris. Lots of tank creatures eat algae or excess food that falls to the bottom of the tank. These can keep the water cleaner so algae doesn't have a chance to get out of hand. Shop around and buy a few of these algae-eaters for your freshwater tank:^{[6]
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- Siamese algae eater
- Twig catfish
- Oto cats
- Amano, cherry, or ghost shrimp
- Nerite, ramshorn, or mystery apple snails

Method 7

Method 7 of 9:
Clean your aquarium once a week.

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Scrub algae off of tank decorations and the inside tank glass. Lift out plastic plants, tank decorations, and large rocks. Don't use soap or bleach on the decorations or the tank since these are really tough on fish. Instead, put all of the decorations into a clean sink and use an algae scrubbing mitt to clean each decoration with warm water. Rinse them to get debris and slime off. Then, use the mitt to scrub the inside glass of the tank.^{[7]
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Expert Source

Aaron Bernard
Fish & Aquarium Specialist
Expert Interview. 17 July 2020.}
- Scrubbing the tank and decorations every week prevents algae from building up and becoming really hard to remove.
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Method 8

Method 8 of 9:
Replace 25% of the water every other week.

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Use a gravel siphon to transfer 25% of the water to a bucket. While you've got the siphon in the tank, move it over the bottom to suck up dirt or debris that can encourage algae to grow. Discard the old water in the bucket and rinse it out. Fill the bucket with fresh water and add water conditioner as needed. Then, let the water sit in the bucket until it matches the temperature of the water in the tank before you pour it back in.^{[8]
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Expert Source

Aaron Bernard
Fish & Aquarium Specialist
Expert Interview. 17 July 2020.}

Method 9

Method 9 of 9:
Keep the tank filters clean.

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Rinse out your filters at least once a month or whenever they look dirty. Algae can start to grow on your filters, especially if your filter hasn't been cleaned in a while. When you replace your tank's water, take out the filter and rinse it clean in the water that you're going to discard. Then, pop it back into your tank before the filter dries out.^{[9]
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Expert Source

Aaron Bernard
Fish & Aquarium Specialist
Expert Interview. 17 July 2020.}
- Remember, don't clean your filters with soap or harsh cleansers since these can be harmful to your fish.
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