JBL ProClean Aqua-Ex gravel cleaner bell

The 10-35 model is a small square bell, 3.5 cm wide and 12.5 cm tall, supplied with 1.5 m of thin pipe. You prime it with a brief suck on the end of the pipe, and its square shape reaches into the corners of small tanks. The 20-45 and 45-70 models have a round bell 4 cm in diameter, 27 cm long and up to 46 cm for the largest, with 2 m of 12/16 mm pipe. Their valve starts the flow when you shake the bell, a shut-off tap stops the water at the end, and the right angle at the end of the bell creates a swirl when you turn it in the substrate.

First place the bucket lower than the aquarium, since the water flows by gravity once the bell has been primed. Then push the bell a few centimetres into the substrate and rotate it: the swirl lifts the sludge, which goes up the pipe, while the grains drop back down. If gravel rises into the bell, lift it slightly, then move on to the next area. On a 60-litre aquarium, a water change of 10 to 15 litres, roughly a quarter of the volume, gives you time to clean a good part of the substrate, and the shut-off valve on the 20-45 and 45-70 models stops the flow when the bucket is full. Finally, rinse the strainer under clean water before putting the bell away.

In the fish tank of an aquaponic system, the sludge that builds up on the bottom breaks down while using up oxygen. The bell removes it during the water change, and the strainer keeps the fish safe from the suction. The organic matter left on the bottom is then mineralised by the filter bacteria, as described in the guide to the nitrogen cycle in aquaponics. The water removed, rich in organic matter, can then be used to water potted plants or garden beds instead of going down the sink. The guide to cloudy water in aquaponics details the causes of water that turns hazy.