Rainbow trout were very much on my mind when I learned that my mother in the US was dying. I mean, we are all gradually dying, but she was dying much faster than most of us are. Enough about that, but I’m glad I was able to see her last year.
I’ve made considerable progress in the last few months on my project in Laos. So much so, in fact, that I was able to indirectly launch about 750 baby tilapia into that place where tilapia spirits dwell after they meet their maker(s). For those of you who follow my blog solely for the entertainment value of my mishaps and misdeeds, this tragedy won’t let you down, but I’m afraid you will have to wait. I’ve got more important things on my mind.
This is kind of a dual-purpose article meant for my readers, of course, but also, through the savvy copy/paste function, for the helpful folks at Aquaponic Gardening. Perhaps they will be able to confirm the extent of my lunacy.
Once my daughter gets her US citizenship sorted out in about 2 weeks, we are going to the US. It’s an expensive trip, so we want to get our money’s worth by staying as long as possible. In regards to my project here in Laos, I’m calling this “The Big Pause.” My generally light load of work for my company in Japan can be carried out just as well in the US, but how do I keep busy and perhaps make some extra cash while there? No, it’s not by lifting 70 pound boxes at the nearby UPS facility 4 hours a day. Since, in terms of theoretical knowledge, I’ve acquired what I consider a PhD level in aquaponics (admittedly, my standards are low), it’s got to involve aquaponics. Aquaponics in the middle of a New England winter? Yes, it does sound nuts.
The greenhouse within the greenhouse
Unless, of course, you happen to have a brother who is not a lunatic and is in possession of at least one 12,000 square foot greenhouse that is in a state of partial use to complete emptiness for 6 to 8 months of the year. Their retail business is only open from early April to the end of October. When I mentioned in an email about the prospect of this idea, I failed to mention that I’m talking about a greenhouse within the greenhouse. He probably thinks I was contemplating heating the entire thing for the sake of a few fish and vegetables. I never heard back about this, so I guess I’ve been taken off his list of relatives sane enough to communicate with.
Here’s a photo of the inside of his greenhouse taken around the middle of March last year. It was a mild spring, so they started earlier than usual. Notice all the structure. The far side to the left faces south. That’s the corner I want to play in. Building this thing must have cost him a fortune. Its got power, water, and, probably, artificial lighting (absolutely necessary). It occurred to me that my brother’s case is probably quite common in cold climates– sweat and toil for half a year, read books and plow people’s driveways for the other half. It also occurred to me that that may just suit them quite fine. So, I started thinking, is this how I can stay roughly half a year in the US each year? It’s completely the wrong way around, though. The idea is to spend cold winters in warm, tropical countries. But one cannot always get his way.
The advantage of a greenhouse within a greenhouse is that the main greenhouse provides all the structure and protection from the nastier elements such as wind and precipitation. This would allow one to literally drape, staple, and fold greenhouse plastic such that a basic enclosure is made.
With nearly two years of exasperation under my belt trying to get things done on a shoestring in one of the world’s least developed (but quaint) countries, I think, thanks to my somewhat skewed perspective, I may have stumbled onto something that could be meaningful to farmers such as my brother. For the potential gain, a system as shown to the right is so cheap to set up that I’m inclined to think that any farmer with unused greenhouse space would be a lunatic not to consider it. Over here in the third world (not Yorkshire, that’s the other third world), we make do with what we have handy, such as bits of twine, empty PET bottles and strips of rubber from used inner tubes. The system shown would require about 1/5th the space of my brother’s greenhouse but it could easily be scaled down such that it would temporarily occupy only about 1/8th. The greenhouse within a greenhouse footprint in this design is about 240 square meters (2,583 square feet). The entire system is composed of 1, 2, and 3-foot high “stick-built” panels with the plywood on the inside. This facilitates bolting the panels together from the outside. It’s just 2 x 4 lumber, like building the wall of a house. There is no floor, or bottom panel. I would put down a layer of newspaper or carpet that’s been thrown away if I can find some. All of these water-holding vessels would be lined with 1 or 2 layers of greenhouse plastic. Only one panel in the entire system will require holes. While the inside of the vessels will be plywood, the outside will be burlap (jute, hessian for my UK and Aussie readers) simply stapled to to the studs and top/bottom plates. Its purpose would be to hold in shredded newspaper– lots of it. So, here we have insulated water vessels for a fraction of what you would buy them for (do a search for insulated water tanks and check out the prices). This whole system would probably take quite some time and effort to build, but after it’s built it would take only a few days to assemble/disassemble each year.
The sump may look unusual, and it will be annoying to have to step over it, but since my brother probably wouldn’t appreciate my breaking up his nice concrete floor to put in a normal, permanent one, I had to come up with something else. The fish tank is 3 feet high (90cm) and the water level would be a bit lower, about 80cm. I wanted to do 4 feet but thought that would be pushing it a bit. The hydroponic troughs (DWC) are 2 feet high; a bit unusual, too, as the water level will be about 50cm. But, within reason, there’s never too much water in an aquaponic system. Besides, there will be living things with claws and such creeping around in there. The sump is 1 foot high and will have a water level of about 20cm. So, what it loses by being shallow, it has to make up for by being somewhat broad. As it is designed, it will hold about 4 cubic meters of water. Orchard/bird netting could be added to help filter fine solids. Water will be moved mechanically only once, from the sump into the fish tank. From there, gravity will take it through the clarifiers into the hydroponic troughs and on back to the sump. Here are some system numbers and the hardware I’m contemplating:
- Fish tank volume: 19 cubic meters
- Hydroponic troughs: 24 square meters each, 12 cubic meters each
- Sump: 4 cubic meters
- Barrel clarifiers: 3 cubic meters total
- Total system water: 74 cubic meters
- Pumps: at least 2 @ 2,000 GPH (7,600 LPH) and a third if it becomes necessary.
- Aeration: one 50LPM air pump for each hydroponic tank and 1 for the fish tank. Some of the diffusers from the hydroponic tanks will go into the sump.
All this trouble for what, ice skating?
No, I hope not. The magic water temperature I’m seeking to hold is 17C, plus/minus a degree. That’s about 62F for you Americans. It will be imperative to use Styrofoam board material on all water surfaces, within reason. Since I’ll be making the greenhouse within the greenhouse as small as possible, this is important for reducing/limiting humidity, too. But when you start thinking of the 74 cubic meters of system water as a heat sink, one becomes more optimistic (until I’m convinced otherwise). An article I read about how to design and construct a greenhouse for use throughout the winter (in Minnesota, I think it was) without any supplemental heating suggested storing as many 52-gallon barrels full of water and painted black in sunny areas in the greenhouse as possible. They warm up during the day and release their heat during the night. That’s to help keep the air warm. I’ve studied before about barrel batch water heating and they are part of my future plans here in the third world. So I incorporated them in my design serving not only to transfer the sun’s energy to the water, but to clarify the water by removing solids. There are 8 pairs of barrels and each will receive water through flexible LDPE tubing. Water enters the top of the higher barrel and enters the lower barrel after making its way underneath a baffle. The same thing happens in the lower barrel and then the water spills into the hydroponic troughs. No moving parts, thank you. Most of the solids will settle to the bottom of the barrels which will have a tap on each to remove them. I forget exactly what angle I set them at in my design, but it’s the same angle that you would tilt your solar panels in the winter in Massachusetts (they face south). I will probably wrap them in clear plastic with some kind of a spacer. Anyway, I’ll be happy if this setup will maintain daytime water temperatures.
The greenhouse within a greenhouse with the passive solar barrel heaters could probably keep the system well above freezing, but I want the water to stay at 17C. To do this, I need supplemental heating. At about $800, this baby can raise my entire system water by 2 degrees in 24 hours. Essentially, this is the contraption that determines how big a system you can have. I wouldn’t suggest to any farmer to invest $10,000 on an efficient outdoor water boiler right from the start. But if this works at the scale I’m contemplating, then an even bigger one would allow expansion and increased income. This is where the real test is. How much of an effect will the passive solar barrel heaters have, what will be the effect of 3 or 4 hours of heat being given off from supplemental lighting, will 35,000 BTU be enough supplemental water heating? I want to find out. What I do know is that there won’t be any need to heat the air what with the great mass of water.
So, what’s so special about 17C (62.6F)?
There are 3 things that make this temperature important. First, it’s the temperature that rainbow trout grow fastest at. Second, it’s an excellent root zone temperature for many cool climate plants. Third, red claw crayfish will not only live and grow (if not thrive) at this temperature, they may just be able to reproduce, too (that would great). If the water temperature drops even rather extremely, it won’t hurt the rainbow trout or the cool climate veggies (it might kill the crayfish, though). But it will slow the growth of all of them.
You all got lucky. I just lost all of today’s work on this article. In fact, I’d finished, pressed preview, and everything I did today disappeared. So, I’ll sum it all up quickly (keeping a copy of what I write in another program!).
My strategy is to overstock the system with fish and then begin to partially harvest them when the system is at maximum capacity. The system can support 950kg of pan-size rainbow trout (just over 300g, about 11 ounces each). Incidentally, that’s at a stocking density of 50kg per cubic meter, well under the commercial density recommended for recirculating tank systems (80kg). So that’s 3,000 fish. I’m going to stock twice that, 6,000 fish. The system will be at full capacity when all the fish are about 100g, or between 3 and 4 ounces. At that point they will be consuming 2% of their body weight per day for a total of 12kg of feed a day. In raft aquaponics, it’s all about the ratio of feed to plant growing area. The advantage of overstocking is that this point is reached in half the time. This gives me 125g/m2. Since I’ll be keeping this as constant as possible by removing fish, say, weekly, the value of the fish removed early will be low, but gradually go up as they are removed later. For the sake of argument, I’m giving these fish an average value of $2.00 each. That’s $6,000. My brother’s business is a family, retail operation which they started way back in 1981, so I presume it will be easy to sell the product to established end-users. Therefore, I’m giving the remaining 3,000 fish a value of $4.50 each (could be much higher). That’s $13,500. I know there will be some fish losses, but let’s just say for now that the fish component of the system is worth $19,500 gross.
For the plants, there are many possibilities here, but let’s take lettuce as an example. Off season and sold retail to a gullible clientele, $1.50 a head. The system can hold 2,304 heads of lettuce. At 5 crops over a 5 to 6 month growing period, that’s 11,520 heads of lettuce at a value of $17,280. Any revenue from the red claw crayfish raised under the rafts in the hydroponic troughs will be a bonus.
I had written a snappy conclusion that would have sold ice to the Eskimos, but it, as well as 5 or so hours of other supporting information with citations and all to convince you that I’m in fact not such a raving lunatic after all, disappeared. So here it is in a couple of sentences. $36,780 would pay for a lot of electricity for supplemental grow lights, pumps, and aerators, as well as quite a few cords of wood. My next step is to cost it all out and apply, through my brother, if he’s willing, for a state or other grant which would allow us to examine the actual feasibility of such a project. It would be meaningful for your average farmer who has a retail (or even wholesale) business and underutilized greenhouse space. He could keep his retail business open a month longer, and open a month earlier; if a wide variety of greens and herbs were grown, perhaps he could even contemplate opening on weekends.
The above proposal is just Phase I. Phase II would add an adjacent mushroom grow room. Air could be circulated between it and the aquaponic system. This would supply the mushrooms with warm(ish), humid air, and the plants with a large volume of CO2 given off by the fruiting mushrooms, improving plant growth (forced CO2 injection is becoming common). Composting worms should be incorporated to turn the fish waste and spent mushroom-growing substrate into valuable worm castings. Extra worms could be fed to the fish. Other schemes to reduce the use of commercial fish feed should be explored.