Keyword – Life and style
Trefwoorden – Houseplants, Gardening advice, Life and style, Gardens
Title – Houseplant hacks: does fish tank water work as fertiliser? | Houseplants | The Guardian
Author – https://www.theguardian.com/profile/gynelle-leon
Link – Houseplant hacks: does fish tank water work as fertiliser? | Houseplants | The Guardian
Publish date – 2026-06-16T09:00:18.000Z
Category – Lifestyle
URL – https://www.theguardian.com/lifeandstyle/2026/jun/16/houseplant-hacks-does-fish-tank-water-work-as-fertiliser

The problem Houseplants need liquid fertiliser, but this can be expensive. Fish tank owners, meanwhile, produce litres of nutrient-rich water during water changes, which then gets poured away. Could it feed houseplants instead?

The hack Water from a freshwater aquarium contains nitrogen, phosphorus and beneficial bacteria. Rather than discarding it during routine water changes, use it to water your houseplants, giving them a free feed.

The method Only use water from a freshwater tank that is changed often. Collect the water during a partial water change. Allow it to reach room temperature before using it on your plants, then apply as you would any water with liquid feed.

The test I used aquarium water on a monstera and a peace lily for a month. Both plants showed healthy growth, and the peace lily pushed out a new leaf. The water did have an odour, but it faded quickly.

The verdict Aquarium water is a useful resource. It will not entirely replace a balanced fertiliser, as the nutrient ratios will vary depending on the tank, the fish and how recently they were fed. But as a supplement between proper feeds, it is considerably less wasteful than watching it disappear down the plughole.