SERIES 17 | Episode 25
Joel Malcolm's suburban backyard is not big but it's extremely productive, with thriving fruit trees and vegetables. It's also no ordinary garden because fish are an integral component. Joel uses a system called aquaponics, where waste water from fish tanks is pumped into gravel filled beds to fertilise his plants. The water is purified during the process and recycled back to the fish.
Joel says he's always had an interest in organic gardening, and while searching the net for permaculture information, discovered aquaponics. "It just made so much sense that I started studying it and building systems from scratch.
"The nutrient rich fish water is pumped through the gravel beds, and the plants extract nutrients out of the water before it's returned to the fish, clean and oxygenated - and the plants grow well.
"The fish give off ammonia which builds up in the water and it can become toxic, so you need to strip the ammonia out of the water. The bacteria grows on the gravel and it then converts the ammonia into nitrogen. The plants use the nitrogen and the water is returned clean.
"Pea gravel is the medium used as it's locally sourced, cheap, free draining, and it provides a great surface area for the bacteria to grow on.
"A number of fish will grow in these systems. I got a great crop of barramundi last year. But try goldfish or coy carp. But check with your local fisheries department to see what's available and what you're allowed to grow in your area. Another two to three months and my fish will be ready."
Joel says that all the material needed to build the aquaponic system is available from local hardware stores. He says it takes two or three months for the bacteria to build up in the beds. "But once the bacteria is built up and the system is in balance, then it's robust and stable."
The water is constantly recycled, so it's actually water efficient. And because there is no seepage, there is no nutrient pollution.
Joel says the system has to be organic because the bacteria in the fish would be affected if any insecticides or fungicides were sprayed into the system. "The only thing that goes into the system is organic fish feed."
There are obviously plenty of nitrates in the water, because things are green and leafy and thriving. But how about trace elements and other minerals that the plants might need? How do they get those?
Joel says they get trace elements out of the fish feed, but if there are any symptoms which show the fish are lacking anything, then chelated iron or seaweed extract are added.
He says: "The system is holistic; the fish, the plants, working together in a natural ecosystem. The water sound is beautiful. It's simple to set up, operate, and maintain."
Aquaponics doesn't have to be expensive. A lot of this system is built from reused materials, and the cost of running the pumps is minimal. Joel also has breeding stock of yabbies - pairs of males and females in the tank to grow next year.
And he's going to feed the fish on worms and duckweed. "The duckweed is growing in with the yabbies, and the worms are growing underneath in bins. The worms will grow on offcuts and scraps from the growing beds of the old vegetables. I'll feed them to the worms and feed the worms to the fish, as well as the duckweed," Joel says.