Aquaponics – Garden Table

I have had a few questions recently about how my backyard improvements were going. Because of a few setbacks, we aren’t going to have a functioning aquaponics system this year. First, we ran into issues with the fish we wanted to raise. The state somehow restricts raising of tilapia, and I have yet to hear back from them what kind of permits I would need. Here’s an excerpt from their May 16th auto-response to me: “Some replies require input from multiple parties, so please be patient.  We’ll  answer your inquiry as quickly and thoroughly as we can.” It’s now July 23rd and I haven’t heard back. I’m expecting the most thorough answer ever. Even if I had heard back, to grow tilapia to a useful size from fingerlings would take longer than I expected (7-8 months), which meant that they wouldn’t have been big enough to eat by the fall even if I had started them when the pond was filled. After that, all of our seedlings died, so we didn’t have anything to grow even if we did have fish. Having no fish garden this year is a little disappointing, but not entirely unexpected. The point of any process is to make mistakes and learn from them. Next year we can start fingerlings early with our seedlings indoors, and have the whole infrastructure ready to go instead of having to figure it out and build it as we go. Which finally brings me to this weeks post.

The last update was about completing the pond. The pond has been successfully holding water for over a month, so that part is a success. The other major component of this system is the grow beds for the plants. Since the pond and all the heavy water is on the ground, the plants in my system will be elevated above the level of the pond. This will allow the water pumped from the pond to water the plants to simply drain back down into the pond using gravity. As I’ve learned by now, you want gravity on your side whenever possible. If you’re having trouble visualizing this, here is the grow table next to the pond with a quick flow diagram superimposed:

The green represents the water from the pond, going to water the plants, and the blue represents the filtered water returning to the pond. Notice how one side of the table overhangs the pond. Water will be pumped from the pond a few times a day up into trays that the plants are in. These trays will have holes in the bottom, so the water can pass through into the table, which is a shallow tub lined with plastic. The bottom is sloped so that the water, now filtered of nitrates and nitrites by the plants, falls back into the pond through this hole.

This detail is kind of interesting. The top of the table has to be level, but the bottom has to be sloped. Also, the structure holding up the trays can’t touch the bottom of the table, or else it would interrupt the flow of water from one end to the other. To accomplish this, I used 2×6 members at the perimeter of the table, and 2×4 members for the crossing pieces. This left 2″ underneath the crossing pieces for me to slope the bottom of the table, which achieves a 1/4″ per foot slope for drainage, which would be fine, except:

Not supporting the plywood in the middle causes it to sag, which makes a pool in the middle instead of draining like I want. I got around this for now by putting the back legs up a little higher than the front and tilting the whole table slightly. Ideally, I would find a way of supporting the plywood in the middle from underneath.

The last thing we need here is a pump and some suitable trays for the plants. The biggest technical hurdle with this is getting electricity out to the pump, but that sounds like a project for another weekend.

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