Aquaponics 101 – More work at the dam.

With the Koi nicely settled into their pond this week and eating lightly, we were able to spend some time at the hatchery site. There are numerous challenges to overcome here and in order to get some clarity I think it would be easier to list them and briefly discuss each of the problems we face.


Birds have now discovered the site and some bird netting is going to be needed soon. We have seen and heard fish eagles and they will easily take out even the bigger fish, and on Tuesday we surprised a comorant perched on the dam wall watching the fish. Being 10km from the sea, this was quite a strange site. The fingerlings were very nervous and swam very closely together in a very tight school. I can’t tell at this stage if I have lost any, but bird netting is now urgent.


Although there is an Eskom transformer close by, this is going to cost money for availability and in any event is not that reliable, which leaves solar and wind power. I have priced a small solar pump at R8000 which, without a battery and inverter seems rather steep. This unit pumps only when there is sun shining directly onto the panel. I could spend a bit more and store power in batteries and then have a more even supply, but I still doubt whether this will give me 12 hours of pumping (½ hour on and ½ hour off) per day. The other option is a wind turbine. We have recently been appointed agents for the Kestrel wind turbine, manufactured by Eveready in P.E. so I will definitely install a test unit at the hatchery site and see how it goes.


I am going to have to give thought to capturing the fish in the big dam pretty soon, but with a 9m diameter and holding about 60 000 L of water this is going to be no joke. Tilapia are fast and very elusive. I came across a brilliant design at my favourite website Backyard Aquaponics  in Australia, for a system of gates. They have been affectionately called “the gates of Ell” after the chap who came up with the idea. What it basically entails is a system of two or more gates hinged in the center of a pond that can be swung together to concentrate the fish in a smaller area. I constructed my first gate this week out of 40mm PVC pipes and fittings and covered with shade cloth. This is what it looks like.


And this is what it looks like in the water.


One has to flood the pipes with water to prevent it from floating to the surface, and we have just attached it to the centre pillar with rope. I will build a second one next week and test it out.

We also continued with our retaining wall of old tyres and I have now decided to have three levels from the top tanks to the bottom level, with a fourth level being right at the bottom where the sump will be. This is what it looks like at the moment.


Next week the big (30m x 10m) greenhouse arrives for the commercial site and we are also getting a second tunnel at the same time which I will be erecting for another client.

Enough for now



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