I am a firm believer in aquaponics as one of the solutions to the food problems we are about to face as a species, and have kept a small aquaponic system for the last year. I’ve kept fish, and planted aquariums for over a decade. I’m going to kind of overview what I’ve learned as I explain what my new aquaponic set-up entails, the material is available from a wide array of sources, but my results will be based on informed observations. I’m taking a more scientific approach, in order to understand the processes involved more clearly, and create repeatable results. The primary focus of this paper is cost of hardware, monitoring equipment, and electrical usage. In addition, I have to deal with water that isn’t the best for aquaponics, and I’ll discuss the problems and solutions in detail.
The premise of aquaponics is the utilization of fish waste to fertilize plants. Fish waste isn’t just fish poop, it’s also the ammonia they excrete through their gills. There is a bacteria cycle that turns the ammonia into nitrite and then into nitrate, which is used by the plants to aid in growth. In an initial aquarium establishment, the bacteria cycle needs to get a foothold. The best places for these bacteria to grow are areas that get immersed and then dried, with as much surface area for the bacteria to grow as possible. The porous clay balls called hydroton are an optimum media for this process, but all the surfaces in an aquarium will help promote this beneficial bacteria. Once the bed is well established, and there are solids building up in the growing bed, one can add red worms to the system, and compost vegetable scraps directly into the grow bed.
After recently putting effort into the establishment of an aquaponic system in the 25 square foot shed attached to my garage, and my inability to mitigate the heat, I’ve decided to bring the system inside where I can keep a better eye on it, and use it to heat the house. I had a great deal of difficulty with trying to bring down the pH, in addition to the problems with the heat, but more on the pH later. On the day the lonely fish I was cycling the tank with finally perished, the water had risen above 90°F, and when I came back from a Murray Hallam and Sylvia Bernstein seminar at the Denver Botanic Gardens, I found my goldfish bloated and floating. The temperature and the irony were both out of control. Time to try again.
The closet that I’m putting this system in is on the second floor of my house in the office. The light is going to bleed out during the morning and evening, but I my neighbors are already aware of my penchant for aquaponic gardening, so I’m hoping it won’t draw too much attention. With the legalization of marijuana for medical use here in Colorado, one of the stipulations is that it can’t be visible to one’s neighbors. I’m going to be growing vegetables and herbs, but I anticipate some suspicion. The space didn’t itself need too much modification, I cut the shelf in half to get the light as high up as possible. The closet is 24″ deep, and 6’10” long. It has no door, just a green cotton curtain.
I switched out the outlet that I’m using for one that has a GCFI, in case anything electrical should inadvertently get submersed. I’m running a Kill-A-Watt meter right out of the wall, into a heavy duty power strip that’s feeding the rest of the system. With this I’ll be able to gauge the exact electrical usage of the system.
This is my first effort towards raising fish that I can eat, rather than tropical pets. Tilapia are my intended livestock, as they’ve been shown to be successful in aquaponics, and quickly grow to edible size. I expect to go from fry to plate in about a year, with a 1 pound fish as the edible size. I’m building this system around a 55 gallon glass aquarium. It is set on 6 glass bricks on the floor (so I can clean around it, and can have the grow bed above it). It has an undergravel filter, and 40# of large aquarium river rock (epoxy coated) gravel. My estimate of the total water in the system is 50 gallons (about 227 liters), accounting for the volume of the gravel, pumps, etc. I’ll start it with 10-12 fry once the tank chemistry is balanced. In doing so I’m following the one pound of fish per five gallons of water advisement, which I’ve heard minor variation on, but certainly seems like a common ratio of fish to water. The fry will be quite small, at first.
The 600 W light that I’m using puts out a lot of heat. As I have it set up now, there’s a small booster fan running air through a flexible 6″ duct, routed out of the closet. The hood for the light is set well high in the closet (2-30# rated drywall ceiling hooks). The electric ballast for the lights is located on a shelf, right next to the intake for the small fan. The lights and fan are running on a timer together. Based on my last experience, the hydroton media tends to get heated by the light, then transfer that heat to the water. I have considered shading the grow bed if this problem arises again, and would be indicated by the grow bed temperature increasing and then the tank temperature increasing correspondingly. I may need to use a deeper bed to mitigate heat as well, and I’ll evaluate as I go. It’s just an example of one of the many variables I’m going to need to account for in this process. Should the heat fall, the tank has a 200 W heater, currently set to the minimum setting of 68°F. It probably won’t see much use until winter. So far the closet isn’t climbing above 87°F, and the water temp has stayed between 74°F and 75.5°F all day. The plant bed has consistently been a half degree higher in temperature than the tank.
For my grow bed, I’m using a Botanicare 21″x21″x7″ bed, listed online as a propagation tray, filled with about 40 L of hydroton. The standard hydroponic bed has an inlet and an overflow fitting. The inlet is filled when a Topfin 30 powerhead is turned on and pumps water into the bed by a 18″ long piece of 1/2″ hydroponic tubing, the pump is on a second timer which alternates on and then off in a 15 minutes cycle. While the pump is running, the bed fills to the overflow level, and returns water to the tank, which is well aerated in the draining process. Filling the bed at the current height takes less that 4 minutes. When the pump turns off, the water back flushes through the feed line, draining the bed completely in a matter of 3-4 minutes. This process helps ensure aeration in the bed by pulling air into it as the water drains. This is a classic approach to a flood and drain system, commonly used in aquaponics and hydroponics for over 2 decades. As a stand for the grow bed I built a simple table from 2 8′-2″x4″s and a 4 foot piece of 2″x6″ cedar, which sets the bed directly over the tank. There is an additional, much more powerful aeration device running constantly as well, a Petco KING 225 powerhead. With this circulation device, the water should be more than adequately aerated. I’m not going to concern myself with dissolved oxygen levels, unless I have an indication that this needs to be tested. Currently the price of the testing equipment is outside the range of what I can put into this system.
30# Rated drywall ceiling hooks (2) – $9.48
600 W Lighting system, bulb, hood, ballast, cords, lowering system – $285.00
188CFM 6″ Hydrofarms booster fan – $44.95
25′ of 6″ ducting with 2 connectors – $19.95
2 additional 6″ connecter rings – $3.00
Growbed – Botanicare 21″x21″x7″ propagation bed – $46.50
flood and drain fittings – $9.99
2′ 1/2″ hydroponic hose – $2.00
Hydroton 50L- $30.00
KING 225 Powerhead – $19.99
Topfin 30 Powerhead – $19.99
Yellow and blue sticky traps for insects – $9.98
200W Heater – $37.49
Undergravel filters (2 29 gallon) – $25.98
Freshwater Master test kit – $31.99
50# epoxy coated aquarium river gravel – $14.99
Indoor-Outdoor thermometer w/min & max readings recorded- $20.47
Digital aquarium thermometer for growbed – $10
55 gallon tank – free off craigslist (tested it outside for 5 weeks, no leaks)
Lumber & hardware for lid – $13.94
Heavy duty powerstrip – $19.99
GCFI outlet – $17.68
diamond plate cover – $2.99
driftwood – $14.00
This adds up to a rather painful truth – $710.36. I’m eager to see how long it takes me to make up for that in system production, with vegetables and fish, rather than Colorado cash crop, I’m guessing it’s going to be a little while. If one went with smaller lighting, this system could be put together for much less, as the lights are nearly half the cost of the system.
For ease of understand the electrical components, I’ve put together a chart showing what is running when. It’s with the attached image files. I took the reading prior to adding the second fan, I’m now seeing daytime readings as high as 956 W on the meter. After taking 2 days to let the system run, and taking the total kilowatt hours used, I’m taking a first estimate of electrical cost. Although my electricity costs different amounts at different times of the day, I’m dividing last month’s total electrical bill of $68.66, by the total usage, 905 kWh, and using the $0.0759 as my cost per kWh. In two days the system used 19.10 kWh for a daily average of 9.55 kWh, or $0.725 per day in electrical cost with my simplified price. Extrapolated, this will cost me a little over $22 a month, but may generate some heat saving during winter.
Now on to the chemistry of my new tank. Dealing with the pH issues isn’t a new thing with my water. Learning your water’s chemical makeup is essential to understanding your own system. If you don’t have a high pH/hard water problem to deal with then this next paragraph won’t mean anything to you, apart from understanding my problem solving approach. Ideal pH for an aquaponic system is advised around 7.0. Unfortunately, the water at my house comes out of the tap with a pH of 8.2 and a total hardness of 300 ppm, really hard, pretty basic water. A simple off the shelf pH lowering product won’t work, as the hardness of the water acts as a buffer and returns it to a high reading after a short time. There are a couple approaches commonly advised for dealing with this problem; 1. hydrochloric acid – which will decrease the hardness and lower the pH, or 2. peat moss and driftwood, which will slowly achieve a similar effect. I’m not in favor of bringing extra chemicals into the house, and I want to learn about affecting pH with peat and driftwood, so that will be my approach. I’m also not in a rush to cycle the tank, so the time spent in this process isn’t wasted. I’ve begun the process with a filter bag full of peat moss, weighted down with stones. I’m using 166 g of peat in my 227 liters of water, amounting to about 7.3 mg/liter. I added this after my first water tests, which indicated a pH of 8.0, at 4:52 PM on 10-6-10. I will also be adding driftwood, but the generalized effect of driftwood wouldn’t be possible to ascertain from this component, as each piece of driftwood has unique properties, related to size, surface area, and chemical composition. The driftwood won’t be here for another few days, so I’ll base what I learn about peat from the limited results I’m able to obtain. I know that I won’t get an ideal pH, so I’ll select fish that can handle a higher pH, and work towards stabilizing it, rather than trying to artificially force it downward. This test was done prior to adding the grow bed to the system. My second test led to an even higher pH of 8.2 at 4:33 PM on 10-7-10 (24 hours later). I cannot explain this result, but think it may be due to salt deposits on the hydroton from being used as the media in the previous system. I’ll continue to monitor and wrestle with the problem. Another 72 hours, 3 tests, and the same consistent 8.2 pH result, I’ll be adding driftwood shortly to bring this number down.
With regards to the rest of the chemical state of the system, I was surprised to find a 1.0 ppm Ammonia content when I did my initial testing (no nitrites or nitrates), the second day’s test led to 0.5 ppm ammonia, and 0.25 ppm nitrites. I think the residual chemical contents of the system can explain the quick ammonia arrival, I did not sterilize this system, it just seemed like too much wasted water, and with this quick start on the biological processes, I’m not feeling I made an error. Through the next few days of testing, the nitrite levels continue to rise as the ammonia falls, and nitrates have appeared. If the pH is still too high when my nitrites and ammonia hit zero, I’ll add ammonia to maintain the bacteria cultures until I’ve got a comfortable environment for my fish. As it is now, I think I’m about a week or two from stocking.