Is Fish Tank Water Good For Plants? 🐠

Is Fish Tank Water Good For Plants

Reading Time: 8 minutes 🍃

The basic aquarium care routine includes changing portions of a fish’s tank water to ensure the fish inside remains healthy and thriving. These water changes may occur weekly, several times a week, or monthly, depending on multiple factors. While dirty fish tank water might not be good for fish, could fish tank water be good for your plants?

Fish tank water is good for plants and can be effectively used as organic fertilizer. Aquarium water has nutrients beneficial to plants, such as phosphorus, nitrogen, ammonia, and potassium, and microorganisms that process them. However, Saltwater fish tank water should never be used for plants.

If you’re thinking about saving your fish tank water for your plants, you’ll be making a smart choice! Continue reading with us as we discuss the benefits of using fish tank water for plants, how to use it, and the things to be cautious about!

Why Is Fish Tank Water Good For Plants?

Fish tank water can help your plants to thrive to their fullest potential, but how beneficial your fish tank water is will depend on your type of plants, how often you clean your aquarium, and the quality of your water. 

Let’s look at the benefits your dirty fish tank water can provide for your plants:

Fish Tank Water Is A Good Form Of Organic Plant Fertilizer

Synthetic fertilizers harm the environment, as their phosphorous levels are much higher than organic fertilizers. By using your fish tank water, you will be preventing the problems which are often associated with synthetic fertilizers. 

Organic fertilizers, such as your fish tank water, reduce the necessity of the repeated application of these synthetic fertilizers to maintain your soil’s fertility.

Fish Tank Water Could Replace Synthetic Fertilizers

Not only is fish water an excellent organic fertilizer, but it could eliminate the need for other synthetic fertilizers! 

Irrigating plants with fish tank water is also ideal for people who only want to grow organic plants. Aquarium water will provide all the valuable nutrients plants require to develop and grow effectively.

Fish Tank Water Is Rich In Nutrients Crucial For Plants

As the fish in an aquarium produces their waste in the tank, it will break down into ammonia, eventually transforming into nitrate and nitrites. 

Because excessive amounts of nitrate in a fish tank could lead to significant health issues in fish, such as stress and growth stunts, it becomes crucial to do regular water changes. 

If the ammonia levels in an aquarium become too high, it could affect the fish’s gills and lead to their deaths. However, these two things, ammonia, and nitrate, which could harm or kill your fish, are exceptional helpers in growing your plants. 

These two nutrients will enrich the soil around your plants and cause your plant’s growth to accelerate greatly. 

Apart from ammonia and nitrate, a fish tank where algae are allowed to accumulate also consists of nitrogen, potassium, phosphorous, and other microorganisms that contain nutritional elements, which help break the other nutrients down. 

When the dirty fish tank water is added to your plants, they are synthesized to generate bolder and greener foliage, which will significantly boost photosynthesis in your plants! This will result in your plants not only looking lively and beautiful but they will perform and being healthier in general.

You may notice that the nutrients in your fish tank water are similar to the ingredients used in soil amendments and plant fertilizer. This makes fish tank water the perfect fertilizer for your plants.

Fish Tank Water Results In Faster Growth

In addition to fish tank water creating brighter and greener foliage, it also boosts plant growth. Dirty fish tank water improves plants’ growth rate mainly because the water is freshly oxygenated, and every plant’s roots need enough oxygen to remain strong and prevent the risk of root rot. 

Fish tank water is also de-chlorinated, allowing more beneficial bacteria in the soil to thrive. Tap water often has trace amounts of chlorine that could influence the health of your plants. 

Lastly, fish tank water also contains large amounts of micro- and macro-nutrients that will feed the plants, resulting in faster growth.

Fish Tank Water Cuts Down On Plant Costs

Using your aquarium water will help you eliminate the extra expenses of owning plants. This includes buying expensive fertilizers, where costs could add up. This becomes especially true if you only have a few indoor or outdoor plants, where buying fertilizer in bulk would not be suitable. 

Buying smaller amounts of fertilizer is often expensive and has no value for money. Fish tank water will significantly reduce your fertilizer cost, if not entirely.

Aquarium water will also eliminate the need to water your plants with hard tap water, which could damage and burn plants if it’s of low quality. 

If clean water is an extra expense for your plants, using your fish tank water will be an ideal option for you financially.

Using Fish Tank Water Is A Form Of Recycling

Not many people know how beneficial their fish tank’s water would be to their plants. This results in dirty fish tank water being thrown down drains, which ends up in the ocean and goes to waste. 

When you use fish tank water to irrigate your plants, you’d be recycling water that usually would have gone to waste. This means you are doing your part in saving the planet!

Cautions When Using Fish Tank Water For Plants

Using your fish tank water could benefit your plants in many ways, but as with all things, you need to be cautious in some aspects. 

Let’s look at the cautions you need to practice when irrigating your plants with fish tank water:

You May Have To Dilute Your Fish Tank Water

If you do not clean your fish tank very often or have neglected to clean the water for a long time, you may have to dilute it before giving it to your indoor plants. 

Some indoor plants are much more sensitive than others, and if your fish tank water is especially dirty, it may be too concentrated. However, it should be suitable if you only plan to use the fish tank water for your garden or any outdoor plants.

Not All Fish Tank Water Is Suitable For Plants

It is worth noting that not all fish tank water can go into your garden plants or houseplants. If you have a saltwater tank, never use this water for your plants, as the high amounts of salt could harm them. 

This becomes especially true if your plants are very young or in pots or containers. The situation will only worsen if these containers or pots have no drainage holes, as the plant’s roots will be forced to use salt water as a primary water source. Only use the water obtained from your fresh water tank.

Fish Tank Water Can’t Be Used For All Types Of Plants

It is not only recommended to save your fish tank water for your ornamental and normal garden plants and flowers, but it’s encouraged! However, using fish tank water to irrigate plants you intend to eat is not a good idea. 

This is especially the case if you have treated your fish tank with chemicals to kill algae or adjust the water’s pH levels. You should not use your fish tank water for plant irrigation if you have treated your fish for any diseases. 

Additionally, if your aquarium water is exceptionally dirty and has not been changed for a long time, it would be best to throw it away entirely, as it may be too concentrated for your plants, and dilution would not be enough.

Fish Tank Water Is Not Suitable If Fish Are Deceased

If any of your fish or aquarium plants have died in the water, which would be a reason for a water change, you should avoid using the batch of water for any of your plants. 

This could cause pests and diseases to spread like wildfire, which could cause you to lose most, if not all, of your plants.

Always Test The Hardness Of Your Fish Tank Water

It is always worth testing the hardness of your fish tank water before you water your plants with it. Your local water source may be hard. 

Hard water contains much more traces of salt and calcium, which could cause the leaves of your plants to wilt or become discolored.

How Should You Use Your Aquarium Water For Your Plants?

Depending on your fish tank’s size and how many plants you have, you can use your aquarium water as the only way to provide your plants with water. 

If you often make partial changes to your aquarium water, you can take water from your fish tank with a sterilized cup as you need it and use the cup to water your plants. 

You can also purchase a large enough watering can and submerge it into the water. If you want the best quality fish tank water, you can stir the sand or stones at the bottom of your tank so it becomes murky. 

This means more nutrients will get mixed into the water, but you may have to dilute it to become useful to your plants, as it will be packed with more nutrients than your plants can hold. However, don’t forget to replace the water as you take it from your tank! 

While following the dosage and timing of your packaged plant food, if you regularly change your fish tank’s water, the water will most probably be diluted enough to apply to your plants for each watering safely.

Using your fish tank’s water to irrigate your plants is not difficult, and if you would like to see how it’s done, check out this helpful video:

Will Fish Tank Water Eliminate The Need For Fertilizer?

After reading all the benefits of why fish tank water is so beneficial to plants, you may wonder if it would work so well that it will eliminate the need for commercial fertilizers. Assuming you have fresh water in your fish tank, the water from the tank will only benefit your plants. 

The fish will do their business in the water, and every leftover food will decompose. When all these elements come together, the water becomes rich with beneficial bacteria and nutrients your plants require to thrive. 

Although your fish water will contain the exact key nutrients you will find in commercial types of fertilizer, your water may be either too rich or not rich enough in nutrients, depending on how often you make water changes. 

The longer you allow algae to fester in your tank, the richer the water will become. However, if you clean your tank as often as five to seven days, there won’t be enough nutrients present to eliminate the need for fertilizer. 

However, it all comes down to quantity. How much water you have available compared to how many plants you have and the intervals of water changes.

If you have a very large fish tank with many fish, along with a couple of aquarium plants, it has the potential to replace fertilizer entirely if you only have a few plants. 

You can use a large amount of water available to provide your plants with both water and fertilizer without ever having to buy commercial fertilizers at an unreasonable price ever again. 

Additionally, when you water plants with tap water, the tap water will have harmful minerals inside of it. 

You may use the same water and treat it for your fish tank, but by the time you use this water to water your garden plants, all these harmful minerals found in tap water will either be gone or have decreased significantly, depending on the mineral.


Fish tank water is highly beneficial to plants, and with all these benefits, it may result in you never throwing your tank’s water away again! Fish tank water has the potential to replace chemical fertilizer completely and benefit any plant, but only if the fish tank is large enough, dirty enough, and there is a small number of garden plants to fertilize!


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