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Imagine having a sparkling, fish-filled pond that provides water for growing fresh herbs and vegetables. With your own aquaponic set-up, you could soon be growing your own edible barramundi, trout or freshwater crayfish alongside the salad you serve them with.
It's an achievable project for anyone and can be very rewarding. Here’s our guide to getting into aquaponics.
What is aquaponics?
There are two main parts to an aquaponic system: a pond, which can contain edible or ornamental fish; and a grow bed for growing plants.
A pump moves water from the pond into the grow bed. The grow bed gradually fills to a set point, at which a siphon valve opens and drains the bed, returning the water to the pond, and the cycle starts again. This is often called a “flood and drain” system.
Colonies of beneficial bacteria will develop quickly in the gravel in the grow bed. These consume waste materials in the water, converting them into liquid plant food. This nutrient-rich mix turbocharges the growth of plants, especially leafy vegetables.
The process also cleans the water, which returns to the pond clean and clear.
What can I raise in my pond?
You can keep virtually any freshwater fish, crustacean or mollusc in an aquaponic pond. Aquaponic systems are great for goldfish and ideal for koi ponds. Koi (which are illegal to keep in ponds in most Australian states and territories) are known for being “dirty”, and an aquaponic system can keep their water clean.
If you want to grow fish to eat there are plenty of options :
- Silver perch – ideal for all regions but the coldest. A perfect choice for beginners.
You can even raise edible marron in your systemTrout – great for cooler zones. They grow rapidly over winter and can reach table size in one season. Can be mixed with larger silver perch.
- Barramundi – more challenging to raise and only suitable for warmer zones or those with long, hot summers as they need warm water in summer to grow.
- Yabbies and marrons – require a little more work and planning but can be very rewarding even if just kept as pets.
- Freshwater mussels – these are edible, but mostly used as natural water filtration.
Be aware that online resources (from overseas) often recommend tilapia, but these are highly invasive exotic fish that are illegal to keep in most Australian states and New Zealand.
Always ensure that your pond walls or edges are sufficiently high and secure so that extreme weather events don’t wash soil or mulch into your pond or wash your fish into drains or creeks that lead to dams or waterways.
What plants can I put in my grow bed?
You can grow other vegetables and annual flowers too, though the results might not be as good. This is because the water tends to be high in nitrogen, which promotes the growth of leaves rather than fruits and flowers.
Every system is different, so it can be a case of trial and error. Add a tomato plant and some strawberries and see how it goes!
You can use regular seedlings from punnets, or more advanced plants. The important thing is to remove the potting mix from their roots. This must be done gently, preferably in a bucket of diluted seaweed solution.
How do I set things up?
You’ll also need a self-activating siphon in or beside the grow bed, connected to an outlet at the base of the grow bed.
There are two common types of siphons, both of which are activated by the water rising:
- Loop siphon – a very simple set-up where a hose is connected to the drain point and turned into a loop, the end of which drains back into the pond. The loop is usually concealed to the rear or side of the grow bed. As water in the bed rises it fills the loop, which then drains and starts a siphon action to empty the bed. The top height of the loop determines the water level in the bed, so it’s easy to fine-tune your operation.
- Bell siphon – a more complicated and specialised unit you can build yourself or buy as modules to suit your set-up. Bell siphons need to be built into the gravel bed itself.
Your siphon must be fine-tuned to drain at the right level. The top 5cm or so of gravel needs to stay dry. The lower part is the “wet zone”, which will constantly fill and drain and be the main root zone.
To get the fill levels right before planting, dig a hole in the gravel so you can see the water level and then run a full cycle. You can then adjust the siphon accordingly
Smaller plants whose roots are mainly in the dry zone may need some manual watering until their roots have grown deeper.
How big should my grow bed be?
Home-garden hobby systems often have a grow bed the same size as the pond. This won’t drain the pond because the gravel takes up at least 75 per cent of the volume of the grow bed. The ideal gravel depth in a bed is about 30cm.
The most common growing medium is pebbles or gravel smaller than 10mm (larger sizes won’t create the pockets for the beneficial bacteria to live in).
All gravel should be thoroughly rinsed so silt and contaminants don’t cloud your pond. Don’t use recycled crushed-concrete gravel as this may affect water pH.
“Expanded clay” products are very useful because of their high surface area but too expensive for the average home system.
Keep it food-safe
If you are growing plants or fish for eating you need to ensure that all materials are food-safe to avoid leaching of chemicals into the water.
Don’t use CCA-treated timber as pond edging, don’t use PVC pond liners, and make sure that your liners or pond-lining paints are labelled as being food grade or “drinking-water safe”.
Let us know if you need a hand with this project, and take a look at these posts for more inspiration for aquaponics and ponds.
You can also check out our step-by-step guides to building a raised garden bed and a pond in a pot.
