Two months ago, I found out that AutoMicroFarm has been accepted into the YCombinator Fellowship program, through the Apply Hacker News experiment. This came as a complete shock to my co-founder and me. In fact, the day we found out we were accepted was my co-founder’s first day at a new job. Unfortunately, a couple days later he told me he needed to step down as a co-founder, and I was flying solo again.
One of my first YCombinator Fellowship meetings was with Luke, the partner at YC specializing in hardware. He urged me to come up with a prototype that utilized only off-the-shelf hardware. My existing plans utilized mostly off-the-shelf parts, except for the vegetable beds and fish tank. A few days later, I stumbled upon the right combination of Google keywords to find wading pools made only of safe high-density polyethylene (HDPE) and at least 12” deep. The material is important because polyvinyl chloride (PVC) is not healthy for the fish, especially fish you may want to eat eventually.
So about a month ago, I got the latest prototype built and running. Here are the parts I used to make the prototype:
I first prepared the place for the prototype by setting up the cinder blocks and the plywood. Note: I would not recommend elevating the vegetable beds. Rather, dig a hole for the fish tank so that the vegetable beds and the fish tank are all sitting on the ground (the fish tank would be in the hole). After getting two circles cut out from the plywood that were the exact size as the pool bottom, I found out that the wading pools deform when water or sand is placed into them, becoming wider at the bottom. I had to widen the circles by cutting them into quarters and adding wood pieces.
When placing the vegetable beds and the fish tank, I made sure to level them and added a ½” (12mm) total slope so that the water would naturally flow towards the edge of the bed where it overlaps the fish tank. The fish tank should be level to maximize the water volume.
I then drilled holes in the vegetable beds, and cut out a rectangular piece of nylon mesh (from a drain sleeve) and taped it with fish-safe tape in order to cover the drain holes. Specifically, I drilled five ¾” (19mm) holes, but I would recommend 20 to 25 ¼” (6mm) diameter holes instead, covering a similar area.
I used coarse sand for the media. The sand is the trickiest part. Ideally, you want to run the five-gallon bucket tests shown in these video series to make sure you won’t have problems with the sand. I didn’t at first, but lucked out after I tested the sand after I had already purchased and installed it. The only problem with it is the large amount of fine particles that (still) make the water dirty. This problem does not harm the fish in any way, and it will go away after a certain time, but it doesn’t look good for now.
Next, I sized and cut ½” PEX tubing, connecting the tubing with various fittings. I made sure to use only stainless steel crimp rings, since copper ones will leach into the water and harm the fish. I finished out the plumbing by drilling holes in the tubing over the sand, and tying them to the vegetable bed sides with zip-ties through holes I drilled for that purpose.
You would think just adding water would be easy, right? Not so fast. Most tap water in the US has chlorine and/or chloramine, both which are lethal to fish. The latter is especially bad news: it takes weeks to dissipate out of the water. Fortunately, I found an activated carbon filter that attaches to a garden hose. The activated carbon removes most of the chlorine and chloramine. You still want to wait a day or two after filling the water tank before adding fish.
I used a pond pump running on an outlet timer six times a day for 20 minutes for the flooding, and one hour and 40 minutes for the draining. The pump does not run at night. The media and the flood-and-drain cycle times are based on the original aquaponics design, iAVs.
After getting feedback on the (lack of) esthetics, I decided to build a fence-like enclosure around the system. Because of earlier design decisions, the enclosure came out rather complicated, costing as much as the system itself. However, there are several ways to simplify the layout and design of the enclosure, reducing the cost. You can read more on the layout options in the last paragraph.
Finally, the prototype AutoMicroFarm system is complete. I am especially excited that the cost of materials of this version of the system came out really low. In fact, this system will pay for itself in six months if it produces at the same yield as the initial barrelponics proof-of-concept prototype (assuming an average fence cost). Compare that to the seven-year payback time for the solar system I got installed at my house… and that is after state and federal incentives!
If you’re interested in buying all the parts needed for this system, I have it for sale on the revamped AutoMicroFarm site. The only parts excluded are those needed to build the enclosure. The site also shows several rendered images of the system in various configurations, both with and without a fence-like enclosure around it. I greatly appreciate any comments you have on this latest version of the AutoMicroFarm system, or any questions, concerns or ideas.