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 may be flushing gold down the toilet. 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. However, 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 it can be used 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. Luckily, that dirty water can actually be beneficial for your plants.

After refreshing the water in your aquarium, don’t simply discard the old water. That water is nutrient-packed 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 all macronutrients essential for plant photosynthesis. 

How to Use Fish Tank Water for Houseplants

Many people take advantage of reusing their aquarium water to water their indoor plants and vegetable gardens. Not only does this save water that would otherwise go to waste, but it also provides supplemental nutrients that limit your need to fertilize.

Plants constantly absorb the nutrients in the surrounding soil as they draw up water. That’s why it’s important to fertilize and replenish potting soil when growing in containers. But when you frequently water the soil with aquarium water, you replace some of these depleted nutrients, giving your plants a boost with easy-to-absorb minerals.  

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 maintaining your aquarium. If you are changing your fish tank water often, using it during each watering session for your plants is safe. Regularly changing your water will prevent the water from becoming too packed with nutrients. 

If you don’t change the water regularly, the density of nutrients can be too intense for standard watering, potentially burning the roots. In these cases, it’s best to use regular water and only water with aquarium water every second or third watering session.

Fish Water and Aquaponics

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. 

Which Houseplants Can You Grow in an Aquarium?

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 aquariums. 

They usually are your big ‘leafy’ and vine houseplants, including:

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

Growing these in your aquarium benefits both 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 also 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:

On Recently Repotted Plants

If you have just repotted your plants with fresh soil, there’s no need to use aquarium water with added nutrients. New potting soil usually has added fertilizer, providing 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 excess nutrients. 

During Cold Weather

Houseplants usually slow growth when temperatures drop, usually during the winter. While the plants are resting, they aren’t growing as much as they do during their active months.

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

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

On 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. 

When 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. 

When There Are 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 has various negative effects: 

  • Dehydrating your plants 
  • Interfering with nitrogen uptake 
  • Stunting growth 
  • Preventing plant reproduction 

Plants exposed to chemicals can suffer from toxicity and die. 

Signs of Overfertilizing in Houseplants

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 overfertilization if nutrients build up in the soil.

These are the signs to look for soon after fertilizing your plants: 

  • Yellow, wilting leaves 
  • Brown leaf tips 
  • Dark brown or rotting roots
  • Leaf drop 
  • Stunted growth
  • 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 with filtered water 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 contains too many nutrients, try diluting it when you start watering again. 

Final Thoughts

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

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

Written by Alexander Picot, Reviewed by Madison Moulton

Alexander Picot

Alexander Picot is the founder of and its lead content writer. He created the website in 2022 as a resource for horticulture lovers and beginners alike, compiling all the gardening tips he discovered over the years. Alex has a passion for caring for plants, turning backyards into feel-good places, and sharing his knowledge with the rest of the world.

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