I came to Rubha Phoil with the understanding that I had DIY skills, interest, and a willingness to deploy them. Ludwig assured me that there were plenty of projects for me to spend my time on. He wasn't kidding.
For the first few weeks I mostly fixed up some urgent issues with huts and caravans. I replaced some old rotting tree stumps that were holding up a small house (!!), put in a column to hold up a sagging awning, fixed a leaky chimney and rebuilt its rain cap that was functioning as a rain *funnel* (#facepalm), and took a diseased tree down.
Ludwig and I sat down to check in after a couple weeks, and I emphasized that I was ready, willing and able to take on any more ambitious projects he might have laying around. He inquired as to my willingness to dig into the aquaponics system and my response was something along the lines of omgyesicanstartrightnowwherearetheparts???
Seriously, an aquaponics system has been on my bucket list for a long time. (Yes, eco permie build projects are the majority of the contents of my bucket list. I used to have vanilla things on it like 'go skydiving' but that's a distraction from builds so I took most of the boring stuff like that off.)
The history of this system is that seven years ago at a different location, Jack, a student at a nearby university, built an aquaponics system for Ludwig as part of his thesis. When Ludwig moved his project here to Rubha Phoil, the aquaponics system came along with but was never assembled.
A few years ago Carlos dug out the pit the system requires inside the poly tunnel, but it's still just been sitting. There's just been a lot of other stuff needing people's attention, and the right person to come along and put it all together hadn't materialized yet. That's where I came in.
What is an aquaponic system?
Aquaculture means fish farming. Hydroponics means growing plants in water instead of soil. Aquaculture systems produce waste from the fish, and require expensive filtration of the water. Hydroponics systems require nutrient inputs for the plants.
An early diagram
Aquaponics puts the two systems together: the waste from the fish tank becomes nutrients for the plants, which form part of a biotic community along with nitrifying bacteria that filters the water which gets recirculated back to the fish. All aquaponics systems will have the following components or features in some form:
Rearing tank.
Where the fishies live. This is a 1,000L tank with the top cut off.
Solids treatment.
A device to settle out solids like fish poop, where it can be easily cleaned out and composted elsewhere. You don't want this stuff in the grow beds. This system uses a Solids Lifting Overflow (SLO) device, which is a barrel with the pipe coming up the top. The bucket allows the solids to settle and drop to the bottom of the tank without getting immediately sucked into the growbeds.
Biofiltration.
Fish produce ammonia, which need to get converted to nitrite and then to nitrate before the water can be recirculated back to the fish. In aquaculture systems, this is accomplished by two kinds of bacteria that live - well, everywhere in the system, but primarily they take up residence in the clay ball medium in the grow beds.
Hydroponics subsystem,
aka the grow beds where the plants will live. These are tanks cut in half and filled with clay balls.
The sump is the lowest part of the system. The pumps live in the sump and recirculate the water back to the rearing tank.
This system is a recirculating, or ebb and flow, system. That means that the growbeds slowly fill with water until a certain point is reached, and then the beds flush completely into the sumps below by means of an autosiphon valve (the device in the middle of the growbeds). This serves to keep the water and the root systems nicely aerated.
Process
The first thing was site prep. The reason Carlos had to dig a deep pit is because there was several feet of peat where the system needed to go. He had to dig down to good solid mineral earth so the tanks, which are very heavy when filled with water, will be on a solid foundation.
All I had to do was find level, set foundation blocks, get a groundwater drain pipe set at the correct elevation, and build planking around the edge of the pit for safety and to control erosion of the pit edge.
The sump header connects all three sump tanks to a common level. When I found it it was all one rigid piece, which required all three sump tanks to be very precisely located in order for the header to attach correctly.
I'm not a big fan of having to 'precisely' place big heavy things like double stacked 500L tanks balanced on cinder blocks in a water filled peat pit of doom, so I cut the header in two places and joined it with rubber couplings. The tanks just need to be close enough, and the header has plenty of wiggle room now.
The old seals on the header were gone, so I ordered replacement Orings. I discovered that measuring, finding, and installing new Orings is an intensely satisfying task.
Next was leveling the site for the rearing tank and SLO filter and getting the foundations set. The rearing tank overflows to the SLO, which overflows to the grow beds, so they all need to be nicely lined up in X Y *and* Z.
Pumps
Gotta move the water somehow. The old pumps were toast, and I didn't like how they were set up above the level of the sump water. Way more friction losses on the inlet side than necessary, which meant the power consumption was higher than necessary. And anything involving cut up bottles of drinking water offends my sensibility of a solid build. So, to the salvage yard I went.
I came up with this solution of housing the pumps inside 4" plastic pipe, running the outlet pipe through the walls, and having the filters as end caps wrapped around chicken wire.
I wasn't terribly excited about the variety of options available for 12v pumps in the flowrates we need, but couldn’t find any better alternatives. The rule of thumb is to change your rearing tank volume over once an hour, which for this system is 1,000 liters per hour (LPH). Two of the pumps I ordered will meet our flow needs, and a third is installed as backup. If the water stops flowing, the fish water goes toxic and they die. And then the plants die. Bummer for you if that's how you get your protein and salad greens. So we have backups. Consequences! Engineering decisions have consequences!
Unfortunately my uneasiness about the cheapo pumps I ordered was well founded. Two of the three developed horrific screeching after only a few hours of runtime. It's the bad bearing screech indicative of old, worn bearings, but these pumps were brand new.
I disassembled them to check the impellers for damage or gunk buildup, but they look fine. I changed the mounting scheme so they were held down by their bases and not suspended by their volutes. No dice. Just cheap stuff, I think. I crawled deeper into the belly of the internet and found some pumps that I think are more appropriate and better built.
Should You Build an Aquaponics System Too?
Probably not, but maybe. Aquaponics systems only make sense if you have very little space, or very little water. It turns out that dirt is actually a really great technology for growing plants, so if you have a bit of dirt as well as enough water, you should just grow plants in that.
Aquaponics systems take a considerable investment in time to build (as I can attest from personal experience), and they take a decent amount of looking after. There are a number of moving parts and equipment failure can cause system collapse if you’re not around to address it quickly. You also may have noticed the considerable amount of plastic involved in this system. If your circumstances don’t dictate the need for an aquaponics system, you probably should do something else.
But if you’re tight on water and/or space, and you’re kind of a nerd and like the idea of fiddling with systems like this, some kind of aquaponics system could be a great project. I’m certainly going to be looking closely at incorporating an aquaponics system into my project back home, where we get less than 10” of rain a year.
How I spent my European holiday