Ok, now for the garden beds. The actual garden beds themselves are made from the tops cut off of the plastic tanks:

However, these will need some support, when loaded with growing medium, water and plants, these will weigh north of 800 lbs. The tanks themselves are only moderately thick plastic, and won't support this weight. Also, I will be casing the whole thing with cedar boards, so I need something to attatch those to. The solution is to build boxes out of 3/4" plywood to hold them.

The boxes themselves are pretty simple:

They are just 48"x40"x13.5" boxes of 3/4" plywood with a hole in the middle for the opening at the bottom of the garden bed. They are reinforced with metal brackets for strength and held together with weatherproof decking screws:

One of the beds is raised up a bit on a platform made of 2x4's. This is really just for aesthetic reasons.

There. I've set the boxes in place, with the liners in them, to see what they look like, and make sure they fit properly. Not bad:

The final step, which I don't yet have pictures of, is to treat the plywood with a coat of outdoor polyurethane ("spar" polyurethane) to help weatherproof it. The plywood isn't going to be directly exposed to the elements, as there will be a cedar cladding on the outside, the plastic liner on the inside, and a cedar cap rail covering the top edge, plywood doesn't weather well, so it's better safe than sorry. Now, while there is such a thing as pressure-treated weatherproof plywood, you do not want to use pressure treated lumber near a fish tank/pond. The copper-based preservatives in modern PT wood are not as toxic as the old arsinic-based ones that used to be used, but fish are very sensitive to copper compounds, and you don't want that leaching into the water.

Next up: Attaching the beds to the frame, plus some misc framing.