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Green Aquarium Water : Quick And Easy Solution

One day I woke up in the morning and saw one of my aquariums has transformed into a pea soup. It was green as it could be. As I faced this problem before I did not over react and I advice you the same. Don’t be alarmed if you got green aquarium water; this is a typical problem that can have many causes and is typically quite simple to repair. 

The first step toward fixing the problem is determining what’s causing it in the first place. There are a few possible culprits. One is a sudden algal bloom in the aquarium. And there are more reasons for this problem.

In this article, we’ll review each one and give you some tips on fixing the problem. You will also learn how to get rid of green water for good so that you can enjoy crystal-clear aquarium water all the time.

Green Aquarium Water

Why Is My Fish Tank Water Green?

The reason your fish tank water becomes green is algae bloom is suspended in the aquarium water. More specifically, it is algae called phytoplankton. Phytoplankton is a type of algae that is very small and can only be seen with a microscope.

Phytoplankton is actually a good thing for your aquarium. It is the base of the food chain and provides food for many different types of fish, invertebrates, and other creatures. The problem with phytoplankton is that it can grow out of control very quickly, causing green water algae to bloom.

But there is another reason for green aquarium water. that is green dust algae. It does not float in your water. Not unless it is disturbed, that is. The water in your aquarium isn’t genuinely green as a result of this. The only reason it appears green is because of the light reflecting off the green dust algae that have colonized every nook and cranny of your aquarium.

Green Aquarium Water

Here I have four pictures of green aquarium water. Can you identify which one is caused by phytoplankton and which one is due to green dust algae? Ya it is that simple. In the left those pictures show you an aquarium coved by green dust algae and in right there is a phytoplankton bloom.

Now you can clearly identify what cause your aquarium to turn green.

What Causes Green Algae In Fish Tanks?

Excess nutrients in the water 

One of the most common causes of green algae in fish tanks is excess nutrients in the water. Algae is a plant, and it needs nutrients to grow. Nutrients, such as nitrates and phosphates, are essential for plant growth. However, if there are too many nutrients in the water, it can cause an algae bloom.

The most common sources of excess nutrients in aquarium water are fish waste and decaying organic matter. If too many nutrients are present, the algae will bloom and overtake the tank, making your aquarium water green.

Poor tank maintenance 

Another common cause of green algae in fish tanks is poor tank maintenance. If the tank is not cleaned regularly, debris and waste can build up, leading to excess nutrients and an algae bloom. In addition, if the filter is not cleaned regularly, it can become clogged with debris and waste. This will prevent the filter from working properly and can also lead to an algae bloom.

Too much light 

Another common cause of green algae in fish tanks is too much light. Algae need light to grow, and if there is too much light, they will grow out of control. If your aquarium is in a sunny location or if you have strong artificial lights, it can cause an algae bloom. In addition, leaving the lights on for too long can also cause an algae bloom. We’ve seen some aquarists that use growing lights on aquariums with no live plants. These lights are not necessary and can actually cause an algae bloom.

Too much CO2 

Another common cause of green algae in fish tanks is too much CO2. Carbon dioxide is essential for plant growth, but if it is too much, it can cause an algae bloom. This is most common in aquariums with live plants. If the plants are not getting enough CO2, they will release it into the water, which can cause an algae bloom.

Green Aquarium Water

Is Green Water Harmful To Fish?

No, As we said before, green water is actually caused by algae, which is a plant. Therefore, it is not harmful to fish. In fact, many fish actually eat algae. However, green water can be harmful to fish if it is allowed to grow out of control. If the green algae bloom is not controlled, it can cause oxygen depletion and lead to fish death. In addition, green water can also block out the sunlight, which can be harmful to fish and plants.

How To Clear Green Aquarium Water

Fixing green aquarium water is not difficult. Fortunately, there are several easy ways to fix green fish tank water.

UV sterilizer

This is by far the simplest and most effective way to clear green aquarium water. A UV sterilizer uses ultraviolet light to kill algae and bacteria. UV sterilizers are very easy to use and are very effective at clearing green aquarium water. In most cases, the water will be clear within a few days.

As for how it works, the water passes through the UV sterilizer, where the UV light kills the algae and bacteria. The water then passes through a filter, which removes the dead algae and bacteria. The only downside to UV sterilizers is that they can be expensive. However, they are very effective and are worth the investment if you have green aquarium water.

Change the water

Another easy way to fix green aquarium water is to simply change the water. This will remove the excess nutrients that are causing the algae bloom. To do this, simply remove 30-50% of the water from the fish tank and replace it with fresh, clean water. You should do this every week or two until the green algae are gone. However, you can’t expect the green algae to disappear fully. You will have to combine this method with one of the other methods mentioned in this list for better results.

Eliminate Light

Eliminating light is one way to get rid of a Green Water algae bloom. To do this, turn the aquarium light off and cover the tank with black plastic, trash can liners, or blankets. Keep it covered for a few days. Uncover the aquarium long enough each day to feed your fish, then cover it up again. The algae bloom will likely die off within a few days using this method; however, you’ll still need to find out what caused the initial bloom. If there’s no change after 48-72 hours, another course of action is needed.


Daphnia is small freshwater crustaceans that are commonly used to control algae in ponds. They are also effective at controlling algae blooms in aquariums. Daphnia is effective at controlling algae blooms because they feed on algae. In addition, they also consume the excess nutrients that algae need to grow. You can buy Daphnia at most pet stores or online. These little critters are very easy to care for and only need to be fed several times a week.

Diatom Filter

A diatom filter is a type of filter that uses diatomaceous earth to remove algae from the water. Diatomaceous earth is a sedimentary rock type that is very effective at trapping algae and other microscopic particles. Diatom filters are very effective at removing algae from the water. In most cases, they will remove all of the algae within a few hours. Diatom filters are easy to use and can be bought at most pet stores. However, they can be expensive.

Chemical Treatments

You can use several chemicals to treat green aquarium water. These are known as algaecides. Algaecides are chemicals that kill algae. They are very effective at clearing green aquarium water. However, they can be harmful to fish and other aquatic life. Algaecides should only be used as a last resort. If possible, you should try one of the other methods on this list before using an algaecide.

Green Aquarium Water

How To Prevent Green Water In Fish Tanks

Preventing green water in fish tanks involves in few steps.

Adequate Lighting

Since the most common reason for algae blooms is too much lighting, you need to make sure that your aquarium is not getting too much light. To do this, you need to ensure that your aquarium is not in direct sunlight. If it is, move the aquarium to a different location. If moving is not possible, you can also cover the aquarium with a dark cloth to block the light.

In addition, you should only have the aquarium lights on for 10-12 hours per day. Any more than that, and you’re at risk of causing an algae bloom. You also need to ensure that you are not using too much artificial light. If you are, you need to reduce the amount of light or the duration of time that the lights are on. If you are unnecessarily using growing lights, you should remove them.

Proper Filtration

Proper filtration is another key to preventing green water in fish tanks. Over time, filters can become clogged with algae and other debris. This can cause the filter to stop working properly. To prevent this, you need to clean your filter regularly. Most filters need to be cleaned every two weeks. However, some filters may need to be cleaned more often.

In addition, you need to make sure that your filter is the right size for your aquarium. If it is too small, it will not be able to keep up with the number of algae in your aquarium.

Regular Water Changes

Regular water changes are another key to preventing green water in fish tanks. Water changes help to remove algae and other debris from the water. They also help to replenish the water with fresh, clean water. Most aquariums need to have a water change every two weeks. However, some aquariums may need to have a water change more often.

When changing water, it’s important to siphon out as much algae and debris as possible. You can do this by using a gravel vacuum or an algae magnet. After you have siphoned out the algae and debris, you need to replace the water that you have removed. To do this, you can use a water conditioner to remove any harmful chemicals from the water.

Testing The Water

Testing the water is another key to preventing green water in fish tanks. Water testing kits are relatively inexpensive and can be bought at most pet stores. Water testing kits allow you to test the ammonia, nitrites, and nitrates levels in your aquarium water. These are all potential problems that can cause algae blooms. By testing the water on a regular basis, you can catch problems early and take steps to fix them. This will help to prevent green water in fish tanks.

Green Aquarium Water

Proper Stocking and Feeding

Proper stocking and feeding are also important for preventing green water in fish tanks. Overstocking your aquarium can lead to an increase in algae growth. This is because there are more fish in the aquarium producing waste.

In addition, overfeeding your fish can also lead to an increase in algae growth. It is because the extra food will settle to the bottom of the aquarium and decompose. This decomposing food will release nutrients into the water that algae can use to grow.

To prevent these problems, you need to ensure that you are not overstocking or overfeeding your fish. You should also ensure that you are feeding high-quality fish food that does not contain many fillers.

Live Aquarium Plants

Live aquarium plants are a great way to prevent green water in fish tanks. Plants help to consume the nutrients that algae need to grow. This helps to prevent algae blooms from occurring.

In addition, live plants also help to oxygenate the water. This is important because algae can consume a lot of oxygen when they are growing. If you are serious about preventing green water in fish tanks, you should consider adding live plants to your aquarium.

Use of Fertilizers and CO2

Supplementing your planted aquarium with excess fertilizers and CO2 can also lead to green water problems. Just like with live plants, algae can use these nutrients to grow. If you’re applying fertilizers or CO2 to a planted tank, keep an eye on how much is being used. Otherwise, you may end up with an algae problem.

Algae Eaters

Another option to prevent green water in fish tanks is adding algae eaters to your aquarium. Algae eaters are fish that consume algae. This helps keep the algae population in check and can prevent algae blooms. Some of the most popular algae eaters include Siamese fighting fish, Plecostomus, and Otocinclus.


Green water in fish tanks can be a major problem. However, there are certain things you can do to prevent it. These include regular water changes, proper stocking and feeding, live plants, and controlling lights. By taking these steps, you can help to keep your aquarium clean and clear.

Do you have green water in your fish tank? If so, what are you doing to prevent it? Let us know in the comments below!

Credit to : KeepingFishSimple

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About Dr.Chamika

Hello, I'm Dr. Chamika. I am a Researcher in Water quality, Aquatic organisms, and Environmental chemistry. I am a passionate fish keeper, with10 years of experience. My mission is to help other aquarists experience the joy of fish keeping.