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Green Algae on Aquarium Glass (And How to Get Rid of It)

Have you spotted some green algae on your aquarium glass? Read on to investigate what it means and what you need to do about it.

Green algae occurs naturally in tanks and is a sign of a healthy ecosystem. Too much algae, however, can be visually disruptive and indicative of excess nitrate levels, overexposure to light, lack of water flow, or overfeeding.

If not dealt with, green algae can take over a tank and cause a range of problems. Keep scrolling to find out what causes green algae and how to deal with it!

Green Algae on Aquarium Glass (And How to Get Rid of It) image

What Is Green Algae?

What Is Green Algae?

Green algae are a common type of algae often found in fish tanks. Generally, green algae is not harmful, usually indicating good water quality and providing some nutrition for fish and invertebrates. 

Snails and shrimp constantly graze on algae, whether it’s on your substrate, decorations, plants, or on the wall of your tank.

Of course, algae is only helpful in moderation. While green algae is the “good” kind, it can still cause problems in your tank. In higher concentrations, free-floating phytoplankton can cause the water to turn cloudy and green.

These conditions arise when conditions are ideal for algae reproduction.

In the fishkeeping world, a sudden growth of algae population is referred to as a bloom, and it’s these blooms that are responsible for disrupting the aesthetic of the tank–not to mention the negative effects on the tank such as nutrient depletion.

What Causes Green Algae in a Fish Tank?

What Causes Green Algae in a Fish Tank

An algae bloom occurs when conditions in the tank are just right for algae reproduction. As with many other organisms, these conditions can include an abundance of food and increased access to light. 

One notable exception to consider is that green algae can occur naturally after the tank has been cycled. 

This is just one side effect of a phenomenon known as “New Tank Syndrome.” As the name suggests, New Tank Syndrome is a general term to describe parasites, diseases, and tank conditions occurring shortly after cycling.

Once the nitrogen cycle is established, conditions in the tank will need several months to truly stabilize. During this time, the tank is at its most susceptible to diseases, parasites, and, yes, algae blooms.

As such, if you notice a sudden onset of green algae right after cycling your tank, you may just need to ride it out. 

Check that there are no conditions in the tank encouraging algae growth (more on that later) and continue to clean the aquarium glass regularly with a sponge, magnetic scrubber, or scraper.

New Tank Syndrome lasts about 6-12 weeks after the cycling process is complete, and during this time, it’s important to test regularly to make sure your tank conditions are stable.

I recommend the API Test Kit since it’s always worked wonders for me helping to identify and address concerns in the tank before they spiral out of control! Keep an eye out for the following causes of algae growth.

Algae Transfer from Other Tank Elements or Fish

Always be careful to quarantine your fish before you introduce them to a new tank environment. Fish can introduce diseases and parasites, as well as algae, to your aquarium. The same logic applies to substrate, plants, or decorations that have been in other tanks and may house algae spores.

Ensure everything transferred from another tank is safely cleaned before introducing it to your new tank environment.

For plants, you can use a solution of hydrogen peroxide and follow these steps:

  1.  Mix 3-5 ml with a gallon of water. 
  2. Soak your plants in the solution for five minutes. 
  3. Soak in dechlorinated water. 
  4. Rinse in clean water.

For best results, quarantine new fish and live plants in a separate tank for 3-4 weeks. Generally, this is done to prevent parasites or diseases, but this process can also help you identify problems with green algae, as well as green algae’s nastier cousins.

With decorations, you can simply soak them in a hot water solution to eliminate the majority of algae. If the problem continues to intensify, consider an algaecide solution, vinegar solution, or bleach solution.


Overfeeding is an extremely common problem in fish tanks, especially for beginners. While it can take some time to establish how much you need to give your fish, a general rule of thumb is that there shouldn’t be any leftover food an hour or two after feeding time.

If there is, adjust the amount you’re feeding or remove the food carefully with a fish net. This leftover food can cause a range of problems in your tank, from ammonia spikes to–you guessed it–algae blooms. 

When there’s too much food in the tank, excess food decomposes and releases nutrients in the water.

An abundance of food prompts the growth of algae, leading to an algae bloom.

Light Exposure

Photosynthesis is an important part of life for many plants and other organisms, including algae. Depending on where your tank is located, as well as how many hours in a day your lights are on, you may find that algae grow at a much more rapid rate in the sun or with strong artificial lights.

Lack of Waterflow

A lack of water flow, sometimes referred to as standing water, is not only harmful to your fish, but it can prompt algae growth. When nutrients aren’t circulated throughout the tank properly, plants can’t get the CO2 they need. Algae, on the other hand, thrive in these conditions and will bloom without adequate water flow.

Nutrient Deficiency

Similarly, if the nutrient balance in your tank is off, your plants may suffer. When plants start to decay, they release an organic compound that algae can feed on. Again, when there’s food in abundance, the algae population can increase exponentially.

Overabundance of Nitrates

Nitrates are the “end product” of the nitrogen cycle in that they continue to build up until you dilute the water in the tank. While not harmful in low concentrations, concentrations approaching 40 ppm or above are toxic to your fish and create ideal conditions for algae spores to grow and thrive.

Other Chemical Imbalances

In addition to high nitrate levels, low phosphate levels or unbalanced CO2 levels can cause algae to grow at a faster rate, causing a bloom.

How to Get Rid of Green Algae on Aquarium Glass

How to Get Rid of Green Algae on Aquarium Glass

If you have a buildup of algae on your glass, then there are several methods you can employ to get rid of it. These methods can be broadly broken down into two categories: dealing with the source and maintaining the algae.

Remember that green algae is a natural part of a healthy tank, and in lesser amounts, all you need to do is maintain your tank occasionally. 

Algae blooms, however,  will not go away over time if there’s an underlying cause that’s prompting faster growth, and you might consider the following methods to get rid of green algae.

Add a UV Filter

A UV filter sterilizes free-floating algae spores, rendering them unable to reproduce. While this will not completely wipe out an algae bloom, it can drastically reduce the algae population. Pair this method with some hands-on cleaning to keep your tank crystal clear.

Use an Aerator

An air pump is a must in the majority of tanks. Poor surface movement means poor nutrient circulation, leading to ideal conditions for algae growth. 

To combat this, consider an aerator like this one by Tetra, choosing a size that fits your tank requirements. It’s one of my personal favorites because it’s quiet and provides good oxygenation and nutrient circulation.

Dilute Nitrates

If your nitrate levels are constantly reaching 40 ppm or above, then it’s likely that you’re not diluting your nitrates enough. To simplify, do a water change more often.

When you do, use a siphon to clean up the substrate, targeting any fish poop, detritus, or leftover food. This helps you get rid of ammonia sources and gas pockets underneath the substrate, which can both lead to unhealthy tank conditions.

Avoid Overfeeding

Overfeeding floods the tank with nutrients and causes a range of harmful side effects. Monitor what you feed your fish. If there’s any food left an hour or two after feeding time, siphon it up or feed a little less next time.

Get the right balance, and you won’t have to worry about algae blooms caused by overfeeding.

Move Your Tank Out of the Sun

It’s not good to have your tank constantly exposed to sunlight. Too much can provide algae with lots of energy via photosynthesis for reproduction.

Simply moving your tank to a different location or reducing the strength or on-time for your artificial lights can work wonders.

Get Live Plants

Live plants are excellent in freshwater aquariums, providing oxygen, hiding places, and making the tank environment more natural. More to the point, plants compete with algae for resources, lessening the chance of an algae bloom.

Maintain Your Tank

As mentioned above, some algae is to be expected in your tank. To remove it from the glass, I recommend this magnetic cleaner. Use it on your glass to clear off algae and leave the cleaner on the corner of the glass when you’re done. No wet hands needed; you can operate the cleaner from the outside of the tank using magnetism.

A scraper blade or a sponge can work wonders for removing green algae from your glass, too. If you need to clean your decorations, get a rough sponge and scrub the decorations thoroughly under hot water.

Use an Algaecide

In most cases, addressing the underlying cause of green algae will resolve your issue. If you start to notice other types of algae setting in, such as black beard algae or brown diatoms, then you might consider an algaecide from Fritz Aquatics

Always be sure to follow the instructions provided for your tank and read the back of the label clearly before use.

Get Some Algae Eaters

Algae eaters are great for keeping your glass clean, but if you’re dealing with a serious algae bloom, they will not keep it under control by themselves; moreover, some algae eaters like Plecos and snails have a higher bioload than people often realize. 

So-called “cleaner fish” still produce waste and must be considered when stocking your tank. Of course, getting an algae eater can help keep algae on your plants, substrate, decorations, and glass under control.


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Do Snails Eat Algae?

Nearly all aquarium snails will eat algae, whether it’s on your plants, decorations, or glass. They can be an effective part of your cleanup crew, but don’t rely on them solely to fix an algae problem, since they will not be able to keep up with an algae bloom.

Does Algae Increase Ammonia Levels?

Algae, contrary to popular belief, does not directly increase ammonia levels; in fact, ammonia creates conditions ideal for algae to thrive, since algae absorb ammonia and other low pH compounds. The result is a higher pH in your tank, which can lead to instability and discomfort for your fish.


Green algae is generally considered beneficial in a tank, but if a bloom occurs, then it’s likely that there’s an underlying issue causing it. 

Overfeeding, lack of surface movement, and light exposure are all common causes for green algae on aquarium glass, and addressing the underlying cause of the bloom, along with some direct care methods like hand-removing algae, algaecides, or a magnetic scrubber will resolve the issue.

Live aquarium plants are very effective at controlling algae in a fish tank. Here’re the live aquarium plants you can keep in your tank to control algae.

Make sure you check out the handy instruction guide above to see how you can keep your tank algae-free and crystal clear!

Photo of author
Prathmesh Gawai
He is the main author and editor at Aquagoodness.com. And he loves to share helpful information on aquarium and/or fishkeeping hobby. Prathmesh has over five years of aquarium and/or fishkeeping experience. Currently, he has a Betta fish tank. He has written hundreds of articles on various aquarium fish species and on fish tank maintenance over the last five years. Connect with him on YouTube here. Learn more about him here.

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