Can You Water Houseplants With Aquarium Water?

Cleaning your aquarium water may be a pain, but it’s necessary if you want to keep your fish alive and healthy. Many people dump the dirty water, unaware they are flushing gold down the toilet. But did you know you can reuse that fish water to feed your houseplants? 

You can water houseplants with aquarium water from freshwater tanks. It’s nutrient-rich and promotes faster, healthy plant growth. It contains potassium, nitrogen, phosphorus, and other nutrients found in fertilizers. If salt, chemicals, or medicine are used in the water, it’s not safe for plants. 

This article will explore the benefits of using aquarium water and how you should use it to fertilize your houseplants. 

Why Plants Love Aquarium Water

As your fish go about their daily life, they do what living creatures do: eat, breathe, and create waste.

When waste and bacteria build-up, it creates a dirty, hazardous environment for your fish to live in. So, after refreshing the water in your aquarium, don’t discard it because that water is fertilizer gold to indoor and outdoor plants. Give your houseplants a refreshing boost by hydrating them with your aquarium water.

The Benefits of Fish Waste

As mentioned in my other article about watering houseplants with bottled water, plants need primary nutrients to go through photosynthesis. 

Much like manure used for fertilizing outdoor gardens, aquarium water is full of beneficial bacteria, nitrogen, phosphorus, and potassium from fish feces. When the waste builds up, microorganisms work like crazy to transform the ammonia toxins into nitrates, a form of nitrogen. Nitrogen, phosphorus, and potassium are essential for plant photosynthesis. 

These three essential nutrients are part of the macronutrients needed by plants, which is why they are found in commercial fertilizers. 

Also, that extra fish food falling through the stones provides extra beneficial proteins—an added plus to your fertilizer water. 

Using Aquarium Water for Houseplants

Many people take advantage of reusing their aquarium water to fertilize their indoor plants and vegetable gardens. 

Plants respond quickly after being fertilized—especially potted plants—due to the soil’s limited nutrients. Plants constantly absorb the nutrients in the surrounding soil, so you must refresh potting soil every few months to keep them fed and happy. When you frequently fertilize the soil with aquarium water, you replace the depleted nutrients and then some. 

And just as the outside greenery appears lush and full of life after a generous rainfall, you’ll notice a difference after you start watering your plants with dirty aquarium water. 

But how often can you water plants with it? 

That depends on how good you are at keeping up with maintaining your aquarium. If you are changing your fish tank water often, using it during each watering for your plants is safe. Regularly changing your water will prevent the water from becoming too dense with nutrients. 

If you’re not noticing a big difference in your pants after watering them with the fish water, there may not be enough nutrients built up for that refreshing boost. 

However, even if you aren’t noticing a big difference, it’s still providing some beneficial nutrients and biological life to your soil. 

Our Ancestors Used Fish Water

Many civilizations throughout history have rooted next to water sources such as rivers, creeks, springs, and other waterways because the land is usually more nutrient-rich from being fertilized by the nearby water.  

Where there’s fish, there’s fish poop! Ancient people learned and reaped the benefits of natural water bodies plentiful with fish, providing food and fertilizer. For the people to survive, their crops must grow strong with healthy yields, so they would haul water buckets from waterways to water their crops or dig canals to route water to their crops. 

Aquaponics Uses Fish Water

Even today, the aquaponics method is widely used as a way to grow plants and crops organically using fish water through aquaculture. This system is designed for plants to rely solely on fish water to provide all the nutrients they need without using soil. Some systems require filtration to keep the ammonia levels down. Others are self-sufficient, with bacteria keeping ammonia levels down. 

Houseplants You Can Grow in Aquarium Water

There are many houseplants you can grow in just water alone, and some of those plants would flourish growing in a vase of aquarium water. As a matter of fact, people have grown them right in their aquarium. 

They usually are your big ‘leafy’ and vine houseplants. 

  • Pothos 
  • Inch Plant 
  • Vining Philodendrons 
  • Monstera/Swiss Cheese Plant 
  • Arrowhead Vine 
  • Lucky Bamboo 

Growing these in your aquarium wouldn’t only benefit the plants and your fish. Many people use plants in their aquariums because the plants absorb the excessive nutrient build-up from fish and food waste. The root systems create a healthier environment by naturally purifying the water and providing hiding places for your fish. 

When To Avoid Fertilizing With Aquarium Water

In general, fertilizing your plants with aquarium water will give them the nutrient kick they need, but there are times when you should avoid using it on your plants. 

Recently Repotted Plants

As with everything in life, there’s a balance, and that applies to the nutrients provided to your plants. If you have just repotted your plants with fresh soil, there’s no need to include fertilization from aquarium water. New potting soil usually has added fertilizer, so it will provide your plants with the nutrients they need for several weeks. 

You’ll want to wait at least six weeks to add aquarium water, or you’ll risk burning the root system from too many nutrients. 

The Dormancy Period

Plants go through a period of dormancy to rejuvenate themselves, usually during the winter. While the plants are dormant, they aren’t growing as they do during their active months.

Your houseplants aren’t exposed to an environment that forces them into full dormancy as they would in a natural habitat. However, they will still go through a resting state as the outside temperature cools and less sunlight is available during the day. 

Fertilizing your dormant houseplants is unnecessary and may cause more harm than good, as your plants don’t absorb as many nutrients as they do during active months. 

Injured or Unhealthy Plants

When your houseplants seem unhealthy, the best thing to do before adding any extra fertilizer is to help them heal. Fertilizing an unhealthy and struggling plant can worsen its condition by damaging the roots while trying to heal itself. Once your plant is up to par, you can resume the previous watering routine with your fish water. 

The Water Is Too Dirty

You don’t want to use the aquarium water if it’s too dirty. If you’ve gotten off track with your water changing routine, the nutrient build-up may be too much, and it can actually burn your plants’ leaves and root system. When there’s an excessive amount of fish poop, it also causes ammonia build-up, which is toxic to fish and plants. 

Additives in the Water

If you’ve added salt or chemicals to the water, do not use them on your plants. Plants naturally absorb small traces of salt from the soil, but too much salt does the following: 

  • Dehydrates your plants 
  • Interferes with nitrogen uptake 
  • Stunts growth 
  • Prevents plant reproduction 

Plants exposed to chemicals can suffer from toxicity and die. 

Signs of Too Much Fertilizer

Yes, too much of a good thing can actually be a bad thing. 

Plants evolved to be resilient, but if they’re suffocated by nutrient-dense soil, they won’t be able to process nutrients, cool themselves, or breathe. 

Your plants will show signs of over-fertilization from nutrients built up in the soil. When there’s a concentration of minerals and other nutrients, it hinders the water uptake from the root system because the roots are suffocated. And when that happens, plants cannot break down the nutrients for energy or circulate the water to cool down, so the leaves will burn and die. 

These are the signs to look for when fertilizing your plants

  • Yellow, wilting leaves 
  • Brown leaf tips 
  • Dark brown or rotting roots system 
  • Leaf drop 
  • Growth stunt 
  • No blooms 

If this happens, lay off the fertilizer for one to two weeks, let your plant heal from the shock, and do the following: 

  1. Pick off all the yellowed and dying leaves. 
  2. Give the soil a long watering to rinse and dilute the concentration of nutrients in the soil. 
  3. To ensure your plant isn’t sitting in soggy water, place your plant on a rag after the excess water stops draining from the pot. The rag will soak up more water, drenching the soil and preventing root rot

If the aquarium water is too concentrated, try diluting it when you start fertilizing again. 

In Conclusion

Having a good understanding of fertilization will help your houseplants thrive in their potted environment.

Aquarium water from freshwater tanks is an excellent fertilizer for your plants that can be used frequently in your watering routine. If you have treated your aquarium water with chemicals, don’t use the water on your plants. 

Your plants will love you for the added boost and develop lush foliage and beautiful flowers. 

Alexander Picot

Alexander Picot is the principal creator of, a website dedicated to gardening tips. Inspired by his mother’s love of gardening, Alex has a passion for taking care of plants and turning backyards into feel-good places and loves to share his experience with the rest of the world.

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