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Green Water for Plants: The Causes and Benefits Explained

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Green water when used to water plants can add valuable nutrients which can help boost plant growth.

Green water is caused by algae. Algae is an aquatic plant that contains chlorophyll which is responsible for its green appearance. High nutrient content in the water and light is key for algae growth and the water’s green appearance which makes it a good source of nutrients for plants.

In this article, we will explain the in-betweens of green water and the nutrients it contains that can benefit plants when watered, even if it has algae.

Is Green Water Good For Plants?

Green Water for plants

Phytoplankton in green water is beneficial to some limits. Phytoplankton like infusoria is cultivated, by many freshwater breeders for sustaining the tiny fry of numerous varieties.

Green water is only dangerous for plants when necessary nutrients are not available to them because they are consumed by green water, so plants might suffer as a result. 

Green water is beneficial for plants in the simplest way as algae release carbon dioxide which is a part of their metabolism, they are responsible for providing carbon dioxide to the water and plants.

High algae in water mean that there are ample nutrients such as nitrogen, phosphorous, and potassium as well as other micronutrients present in the water.

These nutrients are responsible for the algae population and the water’s green appearance in the first place. Therefore, using green water may very well contain valuable nutrients that will be beneficial for plants. 

You may find additional information in our detailed posts on natural sources of water for plants:
Pond Water
Spring Water
Well Water

Rain Water

When applying water to my plants, I use a cost-effective and durable watering can I got on amazon which makes watering fun and easy without making a mess. You can find it by clicking here.

MyLifeUNIT Plastic Watering Can

What Causes Green Water

“Green water” outbreaks are caused by an abrupt increase in phytoplankton population in the water.

Unlike other algae species which grow on the glass or other objects in the aquarium, the green water algae float about in the tank and multiply rapidly, forming what’s known as a ‘bloom’.

Algae blooms can be harmful to aquatic plants and animals not to mention creating an unsightly scenery and in some severe cases can block all the light into the water.

Algae blooms can cause the oxygen concentration in water to drop significantly which in turn will suffocate all living organisms, eventually killing them.

In such a case, green algae water should not be used for plant irrigation as the depleted oxygen concentration may cause unwanted plant problems.

Now we dive even deeper into the causes of what can also make water green.

What Makes Water Green?

Nutrient Imbalance: 

As we all know nutrients are quite important for plants. Algae get nitrogen and phosphate from the fish and their waste which is essential for them.

But do you know when you have too much fish in your tank, or you are overfeeding them, it will result in nutrient accumulation? The same result will happen if you use tap water containing high nutrients.  

Excessive Light:

Being plants, algae love light so much. The availability of higher nutrients in addition to excessive light can cause an algae’s overgrowth making tank water green. Too much light is because of using an intense tank light or bright light is falling on the aquarium from the window. 

Bad Habit Maintenance:

Bad maintenance of habit causes degradation of water quality along with time. With time, a perfect habitat is formed which is suitable for the growth of algae.

Because nutrients aren’t visible so algal bloom or bad health of fish alarm us about the poor habitat condition. 

Chemical Runoff 

Chemical runoff is dangerous because it pollutes our water supply, and causes health issues for humans and animals. The EPA estimates that about 20% of all chemicals used in the United States end up in our waterways.

This includes pesticides, fertilizers, and other industrial waste. If we don’t do something soon, these chemicals could cause serious damage to our environment.

Fertilizers and plant growth chemicals can accelerate the occurrence of green algae water as it provides the ideal, nutrient-rich environment for algae. to quickly proliferate and can turn large waterways green in very little time.

As a result aquatic life will suffer from a lack of oxygen which is used up by the algae.

Are There Plant Nutrients present in Green Algae water?

Green Water for plants

Algae and pond scum contain a high amount of nitrogen which undergo rapid decomposition inside the compost. Pond scum is a fertilizer that provides phosphorus as well as potassium for the compost. Such nutrients are essential for the plants’ growth. 

Additionally, the same nutrients that the algae have used to grow will be present in the water, but in lesser concentrations.

These nutrients can then be used by plants when watered with green water.

Green Water from Fish Tank For Plants

Green, fish tank water can be very beneficial for both house and garden plants. Changing the fish tank water is necessary to ensure the right environment is maintained in order to have happy fish. You can save and reuse the water on your plants.

Watering plants with green fish tank water is beneficial because it contains nitrates, the form of Nitrogen that plants can absorb easily. Plants synthesize nitrates to produce green leafy branches which boost photosynthesis and create the food necessary for healthy growth and development.

The water from the fish tank should not be thrown down the drain. By doing so you are actually throwing away fertilizer which you probably have to get for your plants. There is soo much more to fish tank water than what meets the eye.

The fishes in a tank will carry out their normal day-to-day fishy chores and by doing so, over time, the fish tank becomes dirty and eventually needs to be cleaned.

Water changes are done to a fish tank to remove excess chemicals and other materials that could harm the fish if allowed to build up.

Aged and Green Water from a fish tank may not be beneficial to the fishes afterwards but are definitely beneficial to plants as it contains nitrogen in the form of nitrates.

If you are looking to add vital nutrients to your plants you can use a sure-to-grow plant food.

I have had the best results from using Miracle-Gro Soluble fertilizer. It’s great value for money and will last a long time. You can find it by clicking here.

Miracle-Gro 1001233 Water Soluble

Dangers of Using Green Algae Water for plants:

Oxygen depletion in algae infested water:

As algae produce oxygen through the process of photosynthesis at the time of day but at night, as the photosynthesis stops, algae and many other organisms continue respiring consuming oxygen. During algae blooms on hot summer nights, sometimes the concentration of dissolved oxygen decreases so much for the fish, causing the death of the fish. 

Potential Pathogens in Water:

For plants, algae are not dangerous unless they are properly maintained but sometimes, they have deleterious effects on plants as well as on fish. Algae being an indicator organism creates the conditions favorable for the establishment of plant disease pathogens. Moreover, green algae water acts as a breeding ground and food source for pests like shore flies and fungus gnats. 

How to prevent Water from Going Green?

Although green water has some nutritional value, it’s not too much. Although there are certain ways through which you can prevent water from turning green.

Water Testing:

Performing test on your tank water regularly to maintain check and balance on the nitrate and phosphate levels is essential. In case of their high levels, proper steps must be adopted for their correction. It is better to test your tap water also before using it in an aquarium as nitrate and phosphate concentrations are more in it. 

Deionized water or reverse osmosis is mainly used for the correction of these levels.

Proper Lighting:

Choosing proper light according to the aquarium size and its water depth is quite important.  You should not place your tank in the direct light instead of it placing it in shady places during the day will be effective.  In the case of a bright room, it is better to turn off the tank light during the day. 

Good Maintenance Habits:

For keeping your aquarium healthy, and to avoid algae outbreaks, doing regular water changes will be helpful.  Though, there is a common observation that 50% water change weekly for an aquarium size of 100 gallons is so less water consumption when compared to a 50% changing water for a pond of 2000 gallons. 

Nutrients must be absent in the replacement water. Drain out all surplus food, moreover, the sand should be lightly vacuumed. After a few weeks, do the replacement of mechanical and other filter media. 

Proper Stocking and Feeding:

Overfeeding fish or a higher concentration of fish in a tank result in nutrient accumulation.

According to many people, feeding fish one or two times per day is an efficient way of keeping your aquarium healthy. Moreover, maintaining an adult fish of size having 1 inch in one-gallon water is worthwhile.  However, according to different veteran aquarists, you should avoid feeding your fish every once a week. 

Live Plants:

Using aquatic plants for your tank that consume similar nutrients as algae is also an effective way. You can also reduce light penetration in water by using various floating vegetation. 

Furthermore, such plants will starve the green stuff back to its balance level. This is the reason that aquariums having plants do not have to face algae outbreaks.


Small aquatic organisms called algae are what make water green. Algae can multiply quickly, especially during the summer. This is generally good for the tank because phytoplankton is eaten by small fish. 

However, when there are too many of them in the water, they block sunlight from reaching the plants below and prevent them from growing. They also make the water look green. 

We can make the water in our aquariums healthy and clean by controlling the growth of algae.

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