What’s aqua-what? Hydroponics?

Well, hydroponics is plants in water instead of soil medium. Aquaculture is usually the cultivation of aquatic creatures for food (i.e. fish, prawns, etc). Aquaponics is both together. I think wikipedia has a better description than what I can write (see Wiki entry).

In a nutshell, it’s combining the aquaculture (in my case, Fish) with the hydroponics part. If you’ve kept any fish before, you’d definitely realize that they do produce a fair bit of waste. Otherwise, pet shops won’t be trying to sell you that fancy filter and pump kit plus no matter what, you’d still end up cleaning and changing the water eventually.

Well, let nature do it for you is the name of the aquaculture game. The waste the fishes produce is actually pretty good for plants. So hence my project.

I’ve an outdoor man-made pond with about forty odd Tilapia fishes. They eat and shit a lot. That’s because most of them are edible size by now. Just so you know, these are the 4th generation in my pond (yes, life finds a way to breed) and edible size means over 1.1kg (approx 4.5 lbs). I put a pump in to push the water out into a poly tank what holds hydrokorrels – I can’t find the brand or type I use but this link is pretty close.

The water fills up and gets flushed down and back to the pond. The challenge was that most plants don’t like their roots drowned under water. The roots tend to rot quickly. The solution was inspired by the toilet bowl. Taking some physics lessons, a simple siphon can be created with off-the-shelf PVC pipe parts. This siphon works when the water reaches a certain level. Once the water reaches the right level, it will immediately begin the flush phase where it actually dumps all the water rapidly.

The challenge is to find a fill rate fast enough to trigger the siphon effect but yet slow enough to allow time for the roots to breathe between fill cycles. After some careful tuning, my Laguna 8,000l/hour pump fills my growbed tank in about 10 minutes but dumps the water in 70 seconds.

The diagram is below. Basically the outer 84mm cap is to prevent dirt, leaves and other stuff from clogging the siphon. It does also help you to adjust/tune the water level by creating a barrier to hold the grow bed medium (those hydrokorrels) away from the siphon proper. You won’t need to remove everything just to make adjustments. For the return pipe, the siphon effect is stronger with at least one bend (elbow joint) plus a pipe length of at least half a meter or twenty-odd inches.

Here are my growbed and pond photos.

Adjustment valves to tune the water going into my other filters/hydroponics troughs and the growbed. My 8000L/hr pump is too powerful for a single growbed at the moment.

The return valves/pipes into my pond.

Sweet basil, Thai basil, Mint, rosemary and spinach growing nicely.

The siphon assembly.

My basil and 3 day-old spinach plants. Spinach grows pretty well and fast. I get to harvest them every ten days.

My Tilapia fish. Hardy and dirty. Just what’s needed for the plants. They’re edible too and fast growing.