DIY Backyard Greenhouse Aquaponics Project - Part 3

DIY Backyard Greenhouse Aquaponics Project – Part 3

This post is continued from Part 2. It will make more sense if you go there and read it first. We continue on with the aquaponics build, doing the equalizer and return plumbing, and the bell siphon.

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Not using the bung hole?

At first I was going to connect the aquaponics growbed barrels together through their bungs.

I mean, it’s a threaded hole ready for a connection, right?

Those holes have many problems, though.

One, they are too far in from the bottom edge, and will never drain the last few inches or so of water in the bottom of the beds.

This can make anoxic (oxygen-free) regions that stink and cause problems, i.e. kill plants and fish.

DIY Backyard Greenhouse Aquaponics Project

Two, you get a choice of 2″ or the 3/4″ knockout in the bung plug. The 3/4″ is too small, and I’ll talk about the 2″ in just a minute.

I have seen people use the 3/4″, but I don’t think it’s a good idea. They get plugged up too easily.

Three, the specialty fittings to adapt to anything other than 2″ or the 3/4″ can ratchet up the cost, because you need one for each barrel.

Four, one hole in each barrel (so half of the total number of barrels) is a coarse “buttress” type thread. The big box stores don’t have them, so you have to buy another special adapter online just to get back to a 2″ pipe thread.

The cheapest I found them was $7, and you have to buy them for half of all the barrels. You can find the adapter, called “63mm Coarse Bung Buttress to NPT” on Amazon, but I don’t suggest buying them there.

So I went a different way.

The equalizer

I’m using what I call an “equalizer” in my aquaponics system. Its job is to equalize the water level between the barrels, as well as allow draining through the single siphon.

So the barrels are plumbed together with 2″ PVC pipe, using uniseals through the bottom of the barrels.

A standpipe with drilled holes is inside each growbed, used as a media excluder to drain and equalize the beds.

This goes down through the uniseal to underneath the barrels, where the pipe is tee’d together with other barrels.

I’m using rubber couplings to connect the standpipe to the tee, so maintenance jobs won’t have to involve cutting the pipe.

And between the two sections of the horizontal pipe is a rubber coupling for the same reason.

In this aquaponics system, the water flow works like so:

  1. The fish tank water pumps to the growbeds, and flows through all beds equally using the equalizer pipe
  2. The equalizer pipe also connects to the emergency overflow pipe. This ensures that if the normal siphon drain gets blocked I won’t pump out all my fish tank’s water.
  3. The bell siphon empties the growbeds periodically, and drops back into the fish tank via the return line.

Equalizer drain pipe

Return lines

It’s always a good idea to oversize your return and overflow lines to reduce the chances of biofilm and gunk blocking up your lines.

I used 1″ supply and drain lines, and 2″ lines for the equalizer pipe.

It may be that I need to use a 2″ drain line, but I’m going with 1″ since I’ve seen it working on other people’s systems.

I would have preferred to not use so much plastic, especially PVC, in the system.

HDPE pipe (what the barrels are made out of) is more stable and less likely to crack in freezing weather as well as leach chemicals into the water.

But it’s also more expensive. And the fittings are either expensive or require special heat welding tools to connect.

I think it is possible to make a system with only natural materials. I’m betting a Japanese craftsman working with bamboo could make a really awesome system. But it’s not realistic for me at this point.

The bell siphon

Bell siphonMy AP system is flood-and-drain (AKA ebb and flood) system, and this is is operated by an automatic bell siphon.

Other options like timed pumping can give similar cycling. But considering it’s one more electronic part to fail, I chose not go this route.

My bell siphon is located in the left-hand bed, closest to the far end of the fish tank.

I based the construction partly on YouTube’s Rob Bob’s video. Rob uses a 3/4″ standpipe, but the design he based it on (Affnan) uses a 1″ standpipe.

In the siphon I’m using a 1″ bulkhead fitting, with 1″ standpipe and 1″ to 1-1/2″ reducer adapter. The last piece allows a greater volume of water to flow down the pipe, which helps with initiating the siphon.

You could also heat up the 1″ pipe and expand it to get the same function.

Another important feature is the 90° elbow 8-10 inches below the bottom of the growbed. This restriction also helps with siphon initiation.

Finally, it drains back into the return line.

Next steps

This post continues in Part 4.


OK, that’s all folks! Do you have any questions or comments about aquaponics, sustainable homesteading, permaculture design or anything else? Ask your question down below and let’s talk! You can also use the contact form, or email me at info at thepermaculture dot life.

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