Aquaponics in a Bathtub

Kirsten - Milkwood
Friday, 20th February 2015

With just a few pieces of equipment, the Milkwood team in Australia have created a rooftop aquaponics system in an old bathtub!

Think making your own aquaponics setup would be too hard and costly? Think again my friends. Here's a straightforward and easy way to grow some waterwise greens in your home system.

We made this super easy and downright cheap aquaponics system for the 107 Rooftop Garden in Redfern, Sydney, because we wanted to show folks how straightforward a home aquaponics setup can be.

What is aquaponics?

Aquaponics is a food growing system that utilizes a synergy between fish and plants to create an extremely water-wise growing system. At its most basic, an aquaponics system is a growbed (where the food plants grow) and some sort of fish in a pond or tank.

The nutrient-rich water from the fishpond is pumped into the growbed, where the nutrients are taken up by the plant roots. The now clean and oxygenated water (thanks, plant roots) then drains back into the fish pond, creating happy fish. And around the cycle goes.

On a large scale, the fish (or yabbies) in your aquaponics system can be used for eating. Or, on a small scale like this, goldfish or other hardy freshwater aquarium fish can be used instead, purely for the nutrient they provide the plants. And they're nice to look at.

You can read a brief history of aquaponics here. But back to our pipe-and-bathtub macgyvering.

The basics of the setup

There’s not actually a whole lot to this setup - it’s very simple, and it works really well to produce healthy herbs all through crazy summer heat.

In this context we used a pond for the fish, but you could use another bathtub for the fish tank just as easily. Go with whatever suits your situation, budget and needs.

The bits:

1 metal bathtub
1 small aquarium pump
1 bell siphon (description and how to here)
Some sort of pond (could be another bathtub)
Pebbles or clay beads for growing
Medium pipes cut to size of bathtub dimensions
Fence fittings like these to clip the pipe frame together

Once all the bits were acquired, this aquaponics setup was constructed on the morning of our first planting day at the 107 rooftop garden, by Floyd Constable; fab teacher, bush mechanic and aquaponics nut.

The frame






The pond

This pond was incorporated into the garden gabions we built, with a wooden backing. It’s quite shallow and goes in under the growbed to give the fish a place to hide from the sun and over-enthused visitors.

The pond used basic pond-liner plastic, with a layer of dumpster astroturf underneath to protect the membrane from holes.



The grow bed

There’s really nothing like a good bath. Especially for this purpose. Bathtubs make great home aquaponics growbeds – they’re water tight, strong, and have a nice big hole at one end to let the water out. Perfect.





The plants

The possibilities for planting out a grow bed are fairly endless – people grow everything from herbs to tomatoes to beetroot in them.

For this context, we used whatever plants we had at hand to get the system up and running – ginger, sorrel, beetroots, chives and vietnamese mint (don’t plant mint, by the way – we pulled that out pretty quickly).

Long term, we’ll be planting this with hardy herbs that flourish in good water, and maybe some seasonal veg.


Next steps

Once this bed was planted out, we put some liquid seaweed in the pond water as stand-in nutrient for the plants and left the system to ‘cycle’ for a few weeks before adding the fish.

By the end of the first cycling, the water will be filtered by the plant roots many times and will be clear. It will also have a pH that’s great for the fish that will be put in here - just ornamentals like goldfish or murray river rainbow fish for this setup.

We’ll also add azolla, a small water fern, into the pond. It’s a great fish food and will help keep things balanced. If the azolla goes crazy, it’s a great compost additive, so all good there.

The power load for the small aquarium pump will be maybe $50 over 12 months. The same as a small fish tank. It’s nothing, but given we’ll add very little water to the system over this time, the energy audit is pretty darn good.

Ongoing inputs

Power for small aquarium pump (maybe $50 worth per 12 months)

Occasional fish food

A small amount of water to top up the pond

Not a bad energy input audit! And as a result, we can expect a modest but consistent harvest of greens all year round.

We’re running Backyard Aquaponics Workshops at this space where you can see this system for yourself, and learn how to increase resilience of your food supply using aquaponics at your place.

This article originally appeared here:

Further resources

Also from Milkwood: Capturing rainwater in the city

Watch: Greenhouse aquaponics

Why not buy Ecological Aquaculture - a sustainable solutionfrom our Green Shopping site for a reduced price of £20.79!


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