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.