The invisible workers: how fish waste becomes plant food

Aquaponics joins two things: aquaculture (raising fish) and hydroponics (growing plants in water instead of soil). The magic happens in between, done by living things too small to see.

The loop

Where the bacteria live

The helpful bacteria don't float around in the water. They live as a thin slimy film on every surface: clay balls, gravel, pipes and tank walls. More surface means more bacteria and a system that can handle more fish waste. That's why grow beds are filled with lots of small bumpy balls.

Be patient

A new system can't be filled with fish straight away. It takes about four to eight weeks for enough bacteria to grow. This is called cycling. Rush it and ammonia builds up with nothing to clean it.

Temperature and pH

Bacteria work fastest in warm water and slow right down in the cold. In a New Zealand winter an unheated system does much less. pH tells you how acidic the water is. As the bacteria work, pH slowly drops, so it needs watching. Most aquaponics growers aim for pH close to 7.

Reading the invisible

You can't see bacteria working or nitrate moving into roots. But you can see the signs: fish gulping at the surface when ammonia rises, water turning cloudy, older leaves turning yellow when nitrogen runs short. Test kits turn the invisible into numbers you can graph.