If you’ve been following my trials and tribulations over the last few months, you may be wondering how you could build a small system. I must warn you up front though, that there is no going back, after you’ve built your first system. You WILL become absolutely addicted to Aquaponics. Please don’t say I didn’t warn you.
OK, let’s proceed. I am going to show you how to build a small, single growbed, system. I use this small system to demonstrate the basic concepts of aquaponics to school groups. You probably won’t be raising food fish in such a small system, but ornamentals, like goldfish thrive and there is always a ready market for goldfish. The growbed, however, can provide a small family with plenty of fresh vegetables.
Lets look at the system;
The first element is the growbed. This can be made of anything, but try and give yourself at least 300mm of depth. I have just used a plastic half barrel. Make sure that it is thoroughly washed and rinsed, as you will kill the fish and vegetables with even the slightest traces of chemicals and soaps. Mount the grow bed firmly above your pond as you will be cycling the water back into your pond by gravity.
The pond can be anything from another half-drum to a fish tank or even a garden pond as in the photograph above.
Then buy a submersible pond pump similar to this one.
You will need to get electricity to your site. Please make sure that it is well insulated in a water-proof pipe. You will also need a small plug-in timer. We are designing a flood and drain system, so you will have to pump water for say 15 minutes and then switch off the pump and let it drain for 15 minutes. This is to continually flood the growbed with nutrient-rich water and then suck oxygen to the roots of the plants, every 15 minutes.
How do we achieve this flood and drain? With an auto-siphon. This is what it looks like.
It consists of two pipes (one within the other). The inner one is 40mm – 50mm that goes through the bottom (or side as in the image above). Drill a small (say 6-8mm) hole in the side of the standpipe at the bottom (this is how it drains). At the top cut two v-shaped notches. It makes the overflow flow nicely. The height of this standpipe is the maximum height that the water will rise in your growbed. This should be about 2-3cm below the surface of the gravel (ie. the top layer of the gravel must be dry, but just below the surface it should be damp. The big pipe just fits loosely over the small pipe (75mm – 100mm drain pipe) It’s just there to keep the gravel and roots away from the standpipe. Drill holes at intervals up this pipe.
Then set your pump to be say 15min on and 15min off. The growbed will then fill until it overflows down the standpipe. It will also leak through the little hole at the bottom) ie 95% going into the growbed and 5% draining. When the pump goes off it will now only drain through the little hole at the bottom.
It works best when the pump takes say 10min to get the water to the top of the standpipe and then overflows for 5 minutes, and then takes say 10 minutes to drain through the little hole and 5 minutes dry before the pump comes back on.
If the little hole is too big then it drains too fast and the bed lies dry for too long. If the hole is too small it doesn’t drain all of the water before the next cycle comes on and the plants suffer from root rot. 8mm seems optimal.
If your pump is pumping too fast it fills and overflows too quickly (like in a minute) and then overflows for 14min. This is also too much water. Put in a bypass.
If the pump is pumping too slowly it doesn’t get to the overflow before the pump goes off again and the water doesn’t rise high enough and your plants die from lack of water. Also not good.
If you look at the first picture of the system, you’ll notice that I have a bypass. If you’ve bought a pump that is too powerful, you’ll need to tap off some of this flow. My bypass goes to a simple filter which is just a bucket with a hole in the bottom filled with, from the bottom;
- scrunched up shade-cloth.
- bidden (I think it’ s spelt like this) or foam rubber
It looks like this;
Fill your pond with water and your growbed with 10-13mm gravel and switch it on. I would suggest that you cycle a small system like this, fine-tuning the flow rates for about 5 days, before you add fish or plants. Shade you pond as above so that there isn’t a build up of too much algae. Add some duckweed or aquatic plants.
Then add a few small fish and either sow some seeds directly into the bed (just sprinkle them on the gravel, they’ll fall down the gaps) or plant some good quality seedlings from a nursery. Make sure you rinse off all of the soil from the roots before planting in the gravel. Feed the fish VERY lightly, if at all. If your pond is outside they’ll eat algae and anything else that falls into the pond. This will keep your Ammonia levels down until your nitrifying bacteria build up in the gravel growbed.
You can slowly add more fish and plants to your system as it matures.
Good luck and have fun.