Backyard Aquaponics
A place to discuss aquaponics

For many reasons I've decided to build a 13 meter diameter geodesic dome to house an aquaponics system. This will be the culmination of many years of ideas and whims and components coming together. I'd like it to be a functional space to grow fish and produce to eat, and also an idyllic retreat for relaxing, like those butterfly gardens they have in museums sometimes. In other words, this is not purely a practical space but more of a playground or setpiece.

This dome will have a 40,000 liter, doughnut-shaped tank. I'm guessing that the water temp will maintain around 12-13 degrees C (55 degrees F.) so I am planning to stock trout and catfish.

The doughnut shape is to create a current. I want the combination of pump intakes, return outlets, and powerheads to produce a continuous flow so the trout are constantly swimming in current, as they do in nature. This helps with their health via reduced stress and also adds on muscle. Trout in particular are designed to exist in flow. They are more efficient and happy that way.

I could dig a moat and be done with it. Given the heavy clay soil, I wouldn't even need a liner. I've done this before and it was great. But here's the catch. I want a viewing window. Mainly because I also want an aquarium. Some of my happiest times have been watching trout tanks or shark tanks, and I want that in my life. And it will help me assess the health of the fish in the tank.

Here is a rough idea of what I have in mind.



The idea is to dig out the entire center of the dome, build a circular 1/2m earthbag retaining wall, with the 3m acrylic forming part of the circle. Then lining it all somehow and fulling with water.

The dome development is coming along well. I've obtained a 3m x 1m x 1cm inch slab of acrylic. Now the time has come to figure out if I can actually pull this off.

As you can see attached one idea is to have a liner that completely covers the tank interior. I could do that with a large unbroken membrane that drapes all over everything and is tucked down inside the tank itself. This is the pond approach, which typically uses EDPM rubber liners. Another option is to use laminated polyethylene geographical textiles used to make soil retaining walls, such as 24 mil UV stabilized Dura-Skrim. (https://www.buildsite.com/pdf/ravenindu ... 433858.pdf)

The reason I'm posting here is because I'm looking for ideas of how to create a waterproof seal between liner and window. Silicone sealant adheres well to LDPE, but poorly to acrylic. Weld-on works for acrylic but poorly for LDPE. I don't even know how I'd bond EPDM to acrylic. I used to refer to a chart that describes how to glue one surface to another but I can't find it anymore.

I could create a frame, carefully drill holes in the acrylic, and bolt the liner between the window and frame with some sort of gasket. I could use fiberglass or ferrocement.

I'm putting a drain in the center of the dome floor so if the tank fails, the water will have somewhere to go.

If you have an idea of how I could pull this off I appreciate it!

Not sure would work best for the window.

I think the frame and bolting idea would be the most reliable, but not sure if the pull on the liner would be an issue.

Maybe get a few small pieces of acrylic and build a test seal and see if it is robust and water tight?

In any case I am impressed on the whole idea of your project and would love to see it progress.

Oh there will definitely be tests! LOL I don't want to gamble with 40,000 liters.

I'm wondering whether the span is too long and maybe I should do smaller sections of plexiglas or glass. Also thinking about bracing on top.

Maybe a full frame? top, bottom, sides? vertical bracing every 1 mt?

If you use angle for the frame it would be a lot more rigid than flat.

Though on reflection a curved frame made out of angle would be a challenge

I was just thinking about that too. Also had an idea to use 4x8 foot plywood sheets to match the floorprint of the dome (so 15 sheets for the inner wall, another 15 for the outer wall, plus floor) and basically treat this like a typical large tank with the gasket and glass against the plywood with epoxy paint. I'm not limited at this point although I do think a round earthbag berm is going to be far stronger than any other support I can think of. Just can't figure out that junction between plexiglass and liner....

My advice is do not make the bond between window and liner. Use an intermediate structure (frame). By making an aluminum or steel frame, you can incorporate a lap-seal joint with the liner that leaves an opening for the window. Then you can set the window as you like, using any material desired. Then the seal will be between the window and frame structure.

I wonder how much you will see through the window? The only aquariums I've seen are all glass so the fish have nowhere to hide. It will be brightest in the tank behind the plexiglass and the fish may try an avoid that area. I guess fish species may help along with the water flow and training them to eat there. Interesting to see how it goes.

I will definitely look into this method! Thanks.

Isn't aluminum highly toxic to fish?

I don't know the answer to that question but my guess is they will grow accustomed to the window. Like shy fish in an aquarium who eventually free swim in front of the glass. There also won't be movement there 95% of the time. Will that help or hurt.....?

Food training was my thought as well, making the exit ramp for a BSF feeder end up there. Or making a waterfall feature that causes some nice turbulence in that spot.

I think I would be calling a few plexi sellers and ask about forcing a piece of flat plexi into a curved shape. You're going to have to know the curvature radius to get a good answer, but I'm thinking in bending flat plexi into a curve you're going to see stress cracks. Maybe not at first, but in time. Why not plan for a few vertical flat 3/8" glass viewing windows. Or, maybe a few round porthole style viewing stations. I just think if you intend to spend the money to do a really nice AP setup, you need to make an important design element as durable as possible. Viewing windows in an outdoor fish pond will probably need to be cleaned a lot more often than a little inside aquarium, and plexi doesn't take the scrubbing that glass will without eventually showing unsightly scratch marks.

Hello!

At first I was thinking of a frame made out of 2x4 or 2x6, and along the lines of what DStJohn was thinking.

Something rigid that you can push the window against to make a tight seal. I think his idea of metal is probably better, since it will be more durable in the long run, and more rigid.

I think it might work if it was something like this: Window on the inner water side/ sealant/ liner/ frame/ with stainless steel bolts and nuts with lots of sealant if you use silicone , on the bolts.

If using plexiglass, maybe rounded corners would be good idea, so they don't puncture the liner. From what I've seen, you probably want the bolts to be plentiful/ like every 1.5 - 2 inches.

As for sealing, butyl tape might work. It's used in ponds to tape seams in liners, and I think some of the commercial aquaponic window kits use this.

It's basically like a very sticky rubber, that never dries, so as long as it is held together with bolts, I think it would work very well. I believe it is inert/ non toxic, and fish safe since they use it in ponds.

Or maybe tons of silicone would work just as well.

There are a few window installs floating around on here, it just might take some digging to find them. They might be helpful!

Your plan sounds fun! Keep us updated on the progress!

I think Butyl or similar is a good idea if it is fish safe. I think I have it, at least this is how I would try it. Use an internal double-clamp frame. With this type of setup I think it will be leak free for the long term.

Picture a rectangular frame (or any shape you like). It will be embedded or supported by whatever structure you build. It will have holes drilled and tapped all around to accept bolts, but the holes must not go all the way through the frame.

See the below cross section through a bolt hole. It shows the placement of the butyl sealant, the liner and window and the clamp frame with bolts to squeeze it all together. There are may different variations to build this concept, but I think I have captured the concept, and it will work well.

If you use glass, you will need protection between the clamp and the glass, but this should work well for acrylic. All corners and edges should be rounded smooth. Ideally this would be stainless steel, but steel or aluminum or other materials will work. I recommend a good powder coat or fish safe epoxy paint for protection.

You can make a curved window 3/8 thick by laminating 3 sheets of 1/8". Lay, or press the three perfectly against one another. Then with an eye dropper type applicator run it along an edge with MEK being careful not to over shoot because it not only fuses the too seams together, but will etch any outside surface it touches.

Now you have to make a curved frame to match.
Any recent pics you could share?