Does fish tank water work as houseplant fertiliser?

Houseplants need liquid fertiliser, which can be expensive. Fish tank owners produce litres of nutrient-rich water during water changes that is often poured away. Could that water feed houseplants instead? Water from a freshwater aquarium contains nitrogen, phosphorus and beneficial bacteria.

Rather than discarding it during routine water changes, collect it during a partial change and use it to water your plants. Only use water from a freshwater tank that is changed often. Allow the collected water to reach room temperature before using it, then apply it as you would any liquid feed.

The water may have an odour, but it faded quickly in a test. In a month-long trial using aquarium water on a monstera and a peace lily, both plants showed healthy growth and the peace lily pushed out a new leaf.

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