Polythene on the polytunnel!

Finally, after much work inside and outside the polytunnel over the last few weeks, we have put the polythene onto the tunnel. We only just got there – had a full-on Sunday getting everything ready and then doing it. We haven’t finished yet – one end needs more battens, and we need to put the doors back on. We did manage to do it though, and just in time – the first frost of the season was last night, and while everything outside the polytunnel was frosty, everything inside was just a few degrees warmer, with no frost. Not bad bearing in mind we only got the cover on at dusk, so it didn’t have much time to heat up yesterday.

Here’s what it looked like just after we had finished – showing the fantastic lighting:

Today we’ve started to put the completed growbed stands  in. The growbeds now all have drain holes in their bases and the drains are almost all in place. We’ve even connected all the sumps together (nice big 110 mm pipe). Now I just need to get the tubing and fittings for the drains and inlets and we’ll be ready to start the system up.

Here are some more pics of the growbeds and stands:

Steel & Timber growbed stand:

With growbed in place:

Showing the three linked sumps:

And a frosty growbed sitting outside the polytunnel:

Progress on our Aquaponics

We’ve been a bit silent on progress on the Aquaponics recently. Not because stuff isn’t happening – quite the reverse! We’ve been so busy digging holes for the sumps and designing the growbed stands that we haven’t had a chance to tell you about it.

Here’s the hole for the large sump. It was only supposed to be 500mm deep but at the soil is so good and “easy” to dig I decided to take it down lower – to nearly 900mm. This should allow us to grow plants in the sumps as they’ll all get a bit more light.

And here’s the sump in place:

Having got a little over-keen on the digging for the main sump I then had to drop the other two shallow sumps to the same level. The’re not as deep though, so only about 400mm of digging for these ones:

And here they are, both in place:

Now I just have to connect the three sumps together and we’ll be ready for the growbed stands.

Looking back on it, digging these has been a labour of love. In a lot of ways I’d have been better off designing the system to have them all above ground. However my aim with this system is to get the most use as possible out of the space – so we’ll be trying to grow duckweed, water chestnuts, and possibly taro or wild rice in the sumps to give us true multi-level growing.

Maybe I should have just hired a little digger for the day. Or some Navvies!

Large Polytunnel Aquaponics System

Not sure whether it’s the joy of finally finding a house for us to settle in for the next decade-or-so, or whether it’s the delight at finding a garden that, due to its orientation and terracing, is perfect for a garden split between agricultural and familial duties. Or is it just that spring is in the air? a glorious spring at that!

Whatever it is, my mind is embracing the possiblities of our new situation. A situation that lends itself to a no-holds barred aquaponics system. Gone is my initial timidity. Stuff it, let’s go stright to a BIG system. One that’ll feed the family, and then some.

To maximise its potential, we’re going for a system that is referred to as CHIFT PIST (Constant Height In Fish Tank, Pump in Sump Tank) or CHOP (Constant Height – One Pump). Essentially what this means is that the fish can remain serene, and undisturbed in their tank, with a large sump tank handling all of the variation in water height as water is pumped through to the growbeds. Here’s how it works:

 

• The system starts with the sump and fish tank full of water, and the growbeds empty.
• A timer turns the pump on – the pump is located in or near the sump.
• The pump transfers water from the sump to the fishtank.
• The fishtank overflows, passing water to the growbeds by gravity.
• The growbeds fill with water, while some starts to flow slowly out of the growbeds to the sump.
• With the growbeds full, the timer stops the pump, and the fishtank stops overflowing.
• The water from the growbeds drains under gravity into the sump.

 

So it only needs one pump, a timer, some careful pipework and a sump large enough to handle all of the water from the growbeds.

Following my last post on Greenhouses and Polytunnels we’re going for a HUGE polytunnel. Would love a greenhouse, but for the size that we’re after it’s not in our budget. Here’s our proposed system:

 

Large Polytunnel Aquaponic System

It’s a bit of a monster! Here are the details:

• The fish tank (rear right) is 6′x4′ and 4′ deep – 2700 litres
• There are three rows of growbeds : Ten that are 4′x2′x12″, and three that are 7′x4′x18″ (although these will only be filled to a depth of 12″). 
• Total growbed volume – 4300 litres.
• Growbed:Fishtank ratio is 1.5:1
• The sump is made up of three interlinked tanks,7′x4′x18″. 
• Total sump volume is 3050 litres.
• Sump:Growbed ratio is 0.7:1 

So those are the tech specs, what does it mean for food? This system should provide more than enough fish and non-root veges for a family of four – that’s my estimate, based on other systems I’ve seen. That’s our target – at least from year 2!