DIY Backyard Greenhouse Aquaponics Project – Part 2

This post is continued from Part 1. It will make more sense if you go there and read about the aquaponics project first. We continue on with the budgeting and materials, then growbeds.

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Wood materials boardsBudgeting & materials

Originally when budgeting for this aquaponics project, I calculated around $500 just for purchased wood, then adding pipe, fittings, pump, and hardware.

I’m trying to keep the cost down without having a “cheap” system.

The most expensive individual part will be the EPDM rubber liner for the fish tank, at around $130. I’ll give a final total cost of the project on the last post of this series.

For this project, I used mostly repurposed materials to keep the cost down.

The reclaimed cedar fence section were a big help since they were essentially free and cedar is rot resistant.

This is important in a wet greenhouse environment.

I also really want to be able to operate the aquaponics system in the winter, so insulation and reducing air/water exchange will be important.

This means insulating the supply and return pipes, growbeds, and covering the fish tank and growbeds as much as possible.

Aquaponics fish tank holeDigging the fish tank

This aquaponics setup uses a sunken fish tank and raised growbeds. So I needed to dig out a hole for the fish tank inside the greenhouse.

First, I dug a big hole. This was not super fun, and took quite a while.

I started in the heat of summer, and finished in mid-fall.

The dirt was very hard, and I had to wet it down just to get it soft enough to use a pick.

Unfortunately, wet dirt is heavy. So this made the work even harder than it should have been.

I did get a bucket brigade going one day to knock out a big chunk of it. It really helped to not have to haul the dirt outside myself.

Then I discovered that about 2 feet down the soil turned into slightly decomposed sandstone.

Emphasis on slightly.

So again I had to “water the dirt” and haul it out in buckets. Lather, rinse, repeat.

Finally I got it to the size I wanted. Then realized that the materials I would be using were larger than the hole.

Once more into the breach…to make the hole bigger.

 Building the fish tank form

Fish tank form partialI had some reclaimed cedar fences, and decided to use them for the fish tank form sides. I would have used plywood, but I was trying to not spend money.

The idea was to build a form to hang the pond liner from, then backfill behind the form with dirt.

I also wanted it at least a few inches about ground level to prevent contamination of the fish tank.

The fence sections were cut to length, and screwed together with vertical 2×4 corner posts.

I then leveled the sections starting at one corner and progressing around. Rocks or sandstone bedrock was placed under each corner post for a solid foundation.

Filling dirt and compacting about 6″ behind and in front of the frame stabilized the bottom of the frame.

Fish tank form complete

When refilling I angled the inside dirt to slope towards the center of the tank for easier cleaning.

The fish tank is protected by the greenhouse, and insulated by the earth and its large volume of water, so winter operation shouldn’t be a big concern.

When setting up the fish tank form, I made sure that the top was a few inches above the ground level. I also added a 1/2″ cap rail.

This provides a smooth surface to lay the pond liner over, and helps to keep debris out of the tank.

Building the growbeds

The aquaponics growbeds are raised on posts at a comfortable height. For me this is about waist high.

My initial plan was for 6 growbeds, across the north wall of the greenhouse.

As I said in the last post, I considered making a box then lining it with EPDM pond liner like the fish tank.

Growbed partialBut when I calculated the costs, it would be more expensive to do this than use HDPE barrels.

These barrels usually come in blue or white, and are $15 to $20.

The growbeds have to be strong enough to hold up the weight of water, plants and media (gravel is heavy!) above the ground.

First the ground was packed, leveled and a 12″ square concrete tile put down as a footer for the front posts. The rear posts sit on top of the greenhouse foundation.

On top of that goes the octagonal or oval vertical support posts.

I built a rectangular frame of 2x4s, screwed to the support posts with 3.5″ screws. Cutting notches into the top of the posts allows the horizontal 2x4s to sit on wood.

This was done so all that weight isn’t hanging just by the screws.

The intermediate crosspieces are 2x4s secured using metal joist ties.

Note: I removed these crosspieces later. Keep reading for details.

Finally, it was braced, squared and leveled, though it may make more sense to do that first. I don’t claim to be an excellent carpenter.

Then the barrels are screwed to the crosspieces. Unlike some people who build with barrels, I’m not cutting the barrels in two on a mold seam line.

It can be difficult to cut a straight line this way, but I found a trick on YouTube using intersecting arcs from the seam line. This gives you a good right angle from the seam line.

But wait…there’s more

Then I did some more calculations (and you know how me and spreadsheets get along).

8 barrel grow bedsI realized that I could put in 8 half-barrels (instead of 6) if I took out the 2×4 crossmembers and installed the barrels right next to each other.

This meant I had to unscrew all but one of the barrels and crossmembers, then reassemble the barrels on the frame. I also had to add some 2×4 support to the barrels underneath, since I didn’t want all that weight hanging on just a few screws.

I begrudge re-doing work already completed, but for the 33% gain in bed space (and potential production) the 2 hours it cost was worth the time.

For winter operation, most of the heat exchange takes place in the growbeds. So after the plumbing is installed, they will be insulated with foam board around the perimeter of the growbed, just under the horizontal frame.

Next steps

In the next post we’ll talk about plumbing the equalizer and return lines, lining the fish tank, and installing the pump and aeration.

This post continues in Part 3.


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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