Plants Watered With Fish Tank Water: Using Aquarium Water To Irrigate Plants

By Mary H. Dyer, Master Naturalist and Master Gardener

Got an aquarium? If so, you’re likely wondering what you can do with that excess water after cleaning it out. Can you irrigate plants with aquarium water? You certainly can. In fact, all of that fish poop and those uneaten food particles can do your plants a world of good. In short, using aquarium water to irrigate plants is a very good idea, with one major caveat. The major exception is water from a saltwater tank, which shouldn’t be used to water plants; using salty water can do serious damage to your plants – especially potted indoor plants. Read on to learn more about watering indoor or outdoor plants with aquarium water.

Using Aquarium Water to Irrigate Plants

“Dirty” fish tank water isn’t healthy for fish, but it’s rich in beneficial bacteria, as well as potassium, phosphorus, nitrogen and trace nutrients that will promote lush, healthy plants. These are some of the same nutrients you’ll find in many commercial fertilizers.

Save that fish tank water for your ornamental plants, as it may not be the healthiest thing for plants you intend to eat – especially if the tank has been chemically treated to kill algae or to adjust the pH level of the water, or if you’ve recently treated your fish for diseases.

If you’ve neglected to clean your fish tank for a very long time, it’s a good idea to dilute the water before applying it to indoor plants, as the water may be too concentrated.

Note: If, heaven forbid, you find a dead fish floating belly-up in the aquarium, don’t flush it down the toilet. Instead, dig the departed fish into your outdoor garden soil. Your plants will thank you.

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