DIY Backyard Greenhouse Aquaponics Project - Part 4

DIY Backyard Greenhouse Aquaponics Project – Part 4

This post is continued from Part 3. We continue on with the aquaponics build, now lining the fish tank, adding media and installing final drain/supply lines.

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Lining the fish tank

I used spray expanding foam to fill the cracks between the fence boards. This was to keep dirt from falling back into the fish tank hole before installing the liner, and provide a smoother surface to put the liner on.

The fence boards of the fish tank are uneven, so I also stapled old carpet on the walls to soften the sharp edges.DIY Backyard Greenhouse Aquaponics Project

I was reading about DIY aquaponics, and some people said that using old carpet gave mold a place to grow. Yuck.

So I ripped the carpet out again. It did come out much faster than the time it took to install it.

I’m sure there’s a lesson here about the difference in effort between creation and destruction.

Next I lined the fish tank form with 6oz underlayment (a polypropylene fabric). This is to protect the pond liner from punctures.

Then the pond liner itself. It’s heavy stuff, and stiff when cold. If you can warm it up somehow, do it.

I also suggest you get some help when you do this liner install.

Note: I make this sound much easier than it was. The folds didn’t work out neatly and I had extra material (and folds) to deal with. I’m still not happy with how sloppy the liner looks, but it is functional. Of course, this is what happens when you try to conform a flat sheet to a 3D object.

First I draped the liner over the hole evenly.

Then I got the bottom of the fish tank liner adjusted. It needs to conform to the bottom, and tucked up tight against the walls.

Important: When I bought the liner, I made sure to have about 1 foot of overlap on each side. This was for securing to the wood frame.

Then I smoothed the liner up the walls, getting out all the wrinkles.

Now because this is a flat sheet put into a box, I needed to make “hospital corner” folds on the liner to gather up the excess.

Note that the pocket faces down, not upI didn’t want stagnant water or fish waste sitting in those pockets.

After securing the liner all the way around, I cut off the excess liner.

Cover and final plumbing

After the fish tank is lined, I added a cover sturdy enough to walk on. This involved adding 2×4″ cross pieces every 2 feet or so on a piece of plywood.

I made this into two pieces so it was easier to handle for fish feeding and maintenance.

Then I drilled holes through the cover and attached the final pieces of pipe and hose to the supply and drain lines.

Yes, it looks like the plumbing is kinda in the way now. I wish I had thought about this before putting the barrels here.

But it is where it is, and it should work fine.

Then I ran a “wet test” and put water into the barrels to rinse any residue or debris, check for leaks and proper drain operation.

I only had to tighten up a few worm clamps on the rubber connectors that were slowly dripping.

So far so good!

Growbed media

You have many options when it comes to choosing the media for your growbeds. There’s LECA, or lightweight expanded clay aggregate.

One brand is Hydroton, and is very common in aquaponics though quite expensive.

For my media I bought 1/2″ crushed basalt, called “black and blue” at the rock and gravel supplier.

Ok, so you may know that rock is heavy. This stuff is about a (literal) ton per cubic yard, and I needed 1 yard.

So make sure you have a truck or trailer that can handle this weight.

Gravel washing

I washed the rock with a simple hardware cloth screen over a wheelbarrow, before putting it into the barrel growbeds. This is kind of a pain, and took quite a bit of time and water.

It’s not really required to wash the rock (and some people don’t), but I didn’t want all that dirt in my fish tank or growbeds.

I found a method that worked pretty well, thanks to TCLynx from Backyard Aquaponics forums. Here’s the idea:

1. Set up your working space as much as possible at comfortable height, close to the growbeds. You don’t want to be washing rock bending over, because your aching back will hate you in the morning. Between waist and belly button height worked well for me.

2. Instead of running a hose constantly, I used two water containers. In my case, this was a large cooler on top of a garden cart, on top of cinder blocks. In addition I had an open-top 55 gallon barrel.

3. Use smaller containers to carry gravel in. I used something like these water plant baskets purchased locally. Mine are 10 inches square, which I only half-filled. I dunked these baskets, flipping the rocks a couple times during washing. You will get tired quickly if you’re trying to do this with 5 gallons of rock.

4. Dump your smaller washing containers into a larger container for transport to the growbeds. I used partly-filled 5-gallon buckets. This was 3-4 basket washings.

5. When washing, use successively cleaner water. In one container, wash most of the dirt off, then go to another for final cleaning. This will get the rock cleaner than using the same water container.

6. Occasionally dump and cycle the water containers when they get too dirty. When dumped and refilled that container becomes your new clean rinse, and the other becomes the dirty wash. I swapped back and forth, but do what makes sense for your setup and workflow.

Gravel in growbeds

Bonus: If (like me) you make the mistake of choosing to wash gravel on a day with below-freezing temperatures, 35mph winds and heavy snowfall, make sure to dress warm and use insulated rubber gloves. I found that my cold fingers were happier when washing rock and warmed by the 50°F water.

Also, if you have buckets that are fine except the plastic handles are broken, get some of these BUCKET HANDLES to make carrying more pleasant.

Of course, if you can’t feel your hands it doesn’t really make much difference.

I saw that the 8-foot long 2x4s were bowing from the weight, about 1″ over than distance. Apparently that is too wide of a span for a single 2×4, so I added vertical supports at 4 feet.

This greatly reduced the bending of the 2×4 and seems much more solid.


  • Get help when installing underlayment and liner in the fish tank.
  • Face the corner pockets down, not up.
  • Make a solid cover for the fish tank.
  • Set up a system for washing gravel media.
  • Check level, and adjust as necessary.
  • Gravel media is heavy, so add supports if needed.

This post continues in Part 5.


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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