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Using Aquarium Water for Plants: Easy Way To Boost Growth!

Using Aquarium Water for Plants: Easy Way To Boost Growth!

Do you have difficulty observing your fish because of an algae bloom? It might be necessary to refresh your tank, but is it not wasteful to just discard it?

You may have heard that you can reuse aquarium water on your houseplants, but is this recommended?

Can you use aquarium water for plants? Yes, the nutrients in aquarium water can be beneficial for your plants as the fish excrement and food waste acts as a form of organic fertilizer. A few caveats, however, can make aquarium water unsuitable, such as using saltwater tank water, hard water, and severely neglected tank water.

If the idea of feeding your houseplant babies with algae-laden water makes you go green around the gills, don’t fret.

When used in the right way, aquarium water can be of great use to your plants, your wallet, and the planet! Let’s dive in to learn a little more…

Using Aquarium Water for Plants – What To Know

Fish tank water can aid plant growth, but how beneficial it is will depend on how often you clean your tank, your plants, and the quality of your water.

Benefits of Using Fish Tank Water for Plants

  • It’s a form of organic fertilizer
  • It’s green in more ways than one as you’re recycling wastewater!
  • It can be used on aquatic plants in other tanks/vivariums
  • It cuts down your water/fertilizer bills

Nutrients Found in Fish Tank Water

Allow a full-on green fog of algae (phytoplankton) to accumulate, and your tank water will be housing:

  • Nitrogen
  • Phosphorus
  • Potassium
  • Ammonia
  • and other microorganisms containing trace nutritional elements.

When added to your plants, the nitrates and nutrients in all this natural goodness are synthesized to generate greener, bolder foliage, which in turn boosts photosynthesis!

Does Aquarium Water Replace the Need for Fertilizer?

Though aquarium water contains the same key nutrients you’ll find in commercial fertilizer, the water may be too rich (or not rich enough) in nutrients depending on your refresh schedule.

The longer you let algae fester, the more nutrient rich the water will be, but if you clean the tank as often as every 5-7 days, chances are there won’t be enough nutes present.

So fish tank water can replace fertilizer but only if you have a decent-sized, filthy aquarium and a small number of plants to feed.

When You Should Not Use Aquarium Water on Plants

Aquariums require a deep clean every 6 months and filters to be cleaned monthly, so neglected tanks will contain a harmfully high concentration of nutrients.

Saltwater fish tanks are another no-go, especially for potted plants as salt deposits build up in the soil and burn the roots.

Thirdly, it’s worth testing the hardness of your aquarium water as your local water source may be hard not soft. Hard water contains higher traces of calcium and salt, which can cause discolored, wilting leaves.

What Plants Benefit From Aquarium Water?

If you keep any plants in pots/terrariums such as creeping fig, moss, or golden pothos, they’ll undoubtedly benefit, as will hardy garden plant or houseplant varieties that flourish in nutrient-rich water such as coneflowers, begonias, and tickseed flowers.

Can You Use Fish Tank Water for Tomatoes?

Absolutely! Tomatoes are popularly grown in aquaponic systems that redirect nutrients from fish waste.

Just be aware that tomatoes require specific pH levels and temperatures to prosper, so read this beforehand to help you amend your tank water accordingly.

Is Aquarium Water Good for a Vegetable Garden?

Aquarium water can be beneficial for a vegetable garden, but it may not be the healthiest choice for plants intended for consumption.

Fish tank water will only be suitable for veggies if you don’t use any chemicals to kill algae or treat fish diseases.

Is Aquarium Water Good for Houseplants?

Yes, fish tank water is a good source of natural fertilizer for ornamental flowering plants, especially when applied before their blooming stage as they require more phosphate before they flower.

Just be sure to dilute the water for sensitive varieties.

Is Aquarium Water Good for Succulents?

Yes, potted succulents love richly organic soil and are often fed with seaweed fertilizer, so they will certainly benefit from the nutrients in aquarium water.

Can You Use Aquarium Water for Hydroponics?

You can use aquarium water for hydroponics, but unlike aquaponics, which constantly supplies nutrients, a hydroponic system will not be connected to your aquarium, so this may only be feasible if you have a tank large enough to regularly refill your hydroponic reservoir.

You will also need a biofilter if you use a DWC (Deep Water Culture) system to keep out solid fish waste.

How To Use Aquarium Water for Plants

A fish tank in need of cleaning.

Take small amounts as needed from your aquarium while your fish are still in using a cup or small open-top watering can.

Just be sure to replace the water by preparing a bowl/basin of refill water beforehand. 

Add some dechlorination additive, like this one, and allow 15 minutes for the water temperature to rise to avoid shocking your fishies!

Alternatively, if you want to feed a vast number of house/garden plants, you may decide to siphon the water using a siphon pump.

This can then be transferred to a large watering can, or you could even set up an automated system if you have an extensive container garden.

Related Questions:

Is Fish Pond Water Good for Plants?

Yes, fish pond water is rich in beneficial algae containing nitrogen and phosphate.

Be aware, however, that improper pond maintenance and foreign microbes (decaying foliage, bird droppings etc.) may cause an overabundance of nutrients and affect pH levels.

Can I Put Dead Fish in Compost?

Yes, when mixed with plant waste like leaves, branches, and wood chips, fish carcasses and other meat remains like chicken bones can be added to a hot bin compost.

This composting process is recommended for animal waste as it operates at temperatures between 100 and 140°F to ensure faster decomposition while eliminating odors.


To sum up, murky fish tank water is rich in growth-boosting nutrients that can make your ornamental plants very happy!

Don’t forget that saltwater tanks and hard water are the exceptions as these contain high salt concentrations.

Aquarium water can fertilize veggies too, but this is best used in controlled environments such as aquaponic and hydroponic systems that can amend the water.