10.7 L white food-grade bucket with lid

The first is the water change: the siphon bell fills the bucket while you clean the bottom of the tank, and you empty it outside. The second is soaking, that of a root that needs leaching for several days, with a lid on to keep the dust out. The third is storage, of an opened bag of pellets or a spare grow medium, away from damp.

Keep this bucket for the tank and the pond only, without exception. Write with a marker what it is reserved for, store it with your aquarium equipment and rinse it with clean water only: the smooth wall of the polypropylene does not hold deposits, so a rinse is enough.

The lid also changes the way you store the bucket, since a closed bucket stacks and stays clean between uses. It also prevents splashes when you carry pond water to the house for testing, or water from the tank to the vegetable garden. When full, the bucket weighs nearly 11 kg, since a litre of water weighs 1 kg, which is still a load you can carry in one hand, by the handle, over a few metres. And the day you take a pump or filter apart, it will hold the wet parts so that you don't lose them.

An aquaponic system loses water every day through evaporation and plant transpiration, and this loss is made up with regular top-ups rather than large water changes. The bucket then serves as a preparation reservoir. Tap water contains chlorine or chloramine, which are harmful to nitrifying bacteria as well as to fish gills. Left for 24 to 48 hours in an open bucket, it loses its chlorine through off-gassing and also comes up to room temperature, which avoids a temperature difference when you pour it in. Chloramine, which is more stable, does not escape into the open air: an anti-chlorine water conditioner neutralises it as soon as you fill up, just as it neutralises chlorine if you cannot wait. The article on pond evaporation in summer gives the volumes to plan for.