Basic care for your aquarium includes periodically changing at least portions of the fish tank’s water. Depending on the tank’s size, contents, filter and other factors, water changes may be needed monthly, weekly or even several times a week. Rather than flushing it down the drain, the old water from the tank can be used to water your house plants.

Water from the aquarium is predominantly changed to remove fish wastes and decaying fish food particles. However, it’s those very materials that are beneficial to plants. Aquarium water accumulates nitrogen, phosphorus, potassium and ammonia, plus beneficial micro-organisms for your plants. These are often the same ingredients in plant fertilisers and soil enhancers.

You should however refrain from using water from salt-water tanks because the amount of salt may harm the plants, particularly if they are potted. Likewise, if you’ve used chemicals to adjust the water’s pH level, ammonia or other chemical levels or to treat your fish for diseases, do not use the water for plants being grown for consumption.

Furthermore, 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. If, sadly, you find a dead fish floating 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.