Earlier this year I was hunting around for some sort of fun plant-related summer project to play with, and came across the idea of aquaponics – a closed-loop system that allows you to raise both fish and veggies. I spent a few months geeking out and reading about different ways of doing it, and I learned that you can actually make aquaponics systems that are very small (like desktop sized) or very large (like commercial farms). I learned that I could make a relatively small system without investing too much money
Once the system is established it is almost completely self-sustaining, and it seemed to me that it could be done quite cheaply. In fact, I’ve given myself a budget of $200, and so far have been keeping under it just fine!
Crash course in aquaponics theory
Aquaponics is a combination of aquaculture (raising fish) and hydroponics (growing plants without soil) in a symbiotic system . The fish generate waste, which is converted by bacteria into beneficial nutrients that help the plants grow. When an aquaponics system is balanced properly, it will take care of itself pretty well and only require the owner to feed the fish on a regular basis.
About the nitrogen cycle
In my research, it seems that the most important part of any aquaponics system is the bacteria that converts the fish waste into beneficial nutrients. Fish waste contains a lot of ammonia, which will kill fish if it is not dealt with quick enough. One type of bacteria necessary for aquaponics converts this waste into nitrites, which are actually even worse than ammonia for the fish (and the plants)! Another type of bacteria converts these harmful nitrites into nitrates, which are great for plants and harmless for fish.
Unfortunately for me, all the aquaponics hobbyists I met online say that it takes at least 4 weeks to establish this bacteria before you can really use the system. However, I’ve come across a couple of ideas to help compress this time a little bit so I can get this system up and running as soon as possible.
Ideas to jump start cycling
Every time I tried to discuss methods of decreasing the amount of time it takes to establish this bacteria with aquaponics hobbyists online, I get some pretty discouraging responses. The bottom line is, if I had started working on my system in March, I probably would just fine. But since I am a full-time grad student, I wasn’t really able to get around to doing that, so I need to find ways of improving the cycling time. Here are the things that I’ll be trying:
- Using Nutrafin Cycle to get bacteria into the system ASAP.
- Using worms to help process some of the fish waste.
- Getting some used aquarium filters, tank water and/or used gravel from a local pet store.
Based on the responses I got from online hobbyists, I should pretty much expect all of my fish to die within the first few days of adding them to the system, unless I spend at least a month establishing bacteria. However, everyone that I have spoken with in person around town (pet store fish experts, decorative pond enthusiasts and a nice marine biologist from the Nebraska Game and Parks Commission) have been less conclusive. The fish I’ve chosen (channel catfish) are very tough, and it should only take about a week or so to establish enough bacteria to keep them alive. So, we’ll just have to try it out and see what happens!
Chemical test kits to monitor system health
As mentioned above, the most critical aspect of aquaponics systems is the nitrifying bacteria that converts bad chemicals into good chemicals. To keep an eye on this bacteria I’ll be constantly testing the water and checking the levels of ammonia, nitrites, nitrates and pH. Remember, ammonia and nitrites are bad, and nitrates are good.
If I have high ammnonia, but no nitrites or nitrates, that means that there is absolutely no bacteria present in the system. When I see nitrites, I will know that there is some bacteria present, but not all of the stuff I need. When I see the ammonia and nitrites drop to near zero and the nitrates go up, then I know that the bacteria is present and working just fine. But before I get to that point, I should see the other chemicals all spike and fall periodically.
On Friday I measured the pH to be about 7.8-8.2, which is a bit too high. I’ll be adjusting it to be between 6.0 and 7.0, hopefully more like 6.8 to 7.0. To do this I’ll be using a nice and simple kit from General Hydroponics designed to raise or lower the pH by adding one chemical or another.
Here are the two kits I picked up to help me monitor and manage the important chemicals of the system:
Design of the system
My system is a simple flood and drain system, which means that water from the fish tank is constantly pumped into the grow beds and periodically drained. This allows the plant roots to get access to both nutrient-rich water and oxygen on a regular basis.
The system requires a pump to get water from the fish tank up into the grow beds, but there are all sorts of clever mechanical systems that can be used to get the water back down to the fish tank after some amount of time. Bell siphons are really popular, but I love the simplicity of the loop siphon. It is literally a loop of tubing that fills with water as the grow beds fill up, until water reaches the highest point in the loop. Eventually all the air in the loop is pushed out, which causes water to be sucked into the loop until it finds air. It’s hard to explain, but I’ll post videos later!
I used Sketchup to come up with a simple design to follow:
- Fish tank (FT): a 110 gallon stock full of water for the fish to swim in.
- Grow beds (GB): a 55 gallon barrel cut in half and filled with pea gravel for the plants to grow in.
- Pump + plumbing bits: transfers the water from the fish tank into the grow beds.
- Loop siphons: to automatically drain the grow beds without any electricity required.
And here are the sources for all those bits:
Acquiring and filling the stock tank
Picking up the 110 gallon stock tank for the fish tank was interesting. It is quite large, but I was able to somehow wedge it into the trunk of my Buick LeSabre. And by “somehow” I mean it was mostly hanging out. But I was able to transport it to the site by driving very slowly and carefully!
I filled the stock tank with tap water and waited two days for the chlorine to escape. On the first day I noticed bubbles clinging to the tank, which tells me the chlorine was indeed off-gassing!
Installing the pump and plumbing
To transport the water from the fish tank to the grow beds I installed a 185 gallon-per-hour pump and some black vinyl tubing from a local hardware store. Luckily it was actually really easy and cheap to connect the pump the vinyl tubing, then split it into two outlets for the grow beds – just a single tee junction and a hose clamp.
One of my favorite things about the pump I bought is that it is submersible, so I don’t need to have any extra tubing going into it – just drop it in the tank! It is also really, really quiet, so the fish should be pretty happy.
Building a temperature probe
Last summer was very, very hot here in Nebraska so I’ve been a bit concerned about the water temperature of the fish tank. Temperature plays a big role in the metabolism and efficiency of both the fish and the bacteria, so it is important that it doesn’t get too hot (or cold).
The location of my aquaponics system is on a south-facing concrete deck next to a brick building at my university’s campus. Funnily enough, the part of the building that the system is sitting outside is the campus glassblowing studio, so hot temperatures are to be expected!
To keep an eye on the water temperature, I hacked together a super simple temperature probe using a thermistor and an Extracore RST that I had laying around just for this type of project. The thermistor is set up in a basic voltage divider and fed to the Extracore for analog reading. The Extracore just takes readings, converts the data into usable Fahrenheit temperature values and outputs it to the serial port. Anytime I want to read the temperature of the water I can just plug in a 5V FTDI breakout board to my laptop and open up the Arduino IDE’s Serial Monitor!
On the day that I installed the sensor I measured the water temperature to be around 70F. I’ll be keeping an eye on it to see if I am measuring it correctly next week!
The highest priority right now is getting bacteria established in the system, but I can’t start doing that until I’ve got my grow beds set up. A lot of bacteria will grow on the gravel of the beds, so I really need to have the whole system up and running before any bacteria show up.
I’m hoping to have the grow beds on Monday morning, then turn them into grow beds and build a wooden framework to contain them as soon as possible. My goal is to have the grow beds installed and water flowing by the end of the day on Tuesday. That leaves only 7 days or so to establish bacteria before my channel catfish arrive from Arkansas, which sounds like a pretty bad scenario.
I think I’ll prepare a few extra barrels with dechlorinated water so I can move the fish around and dilute the water of the main fish tank. I am still expecting the fish to die within the first week or so, so I’m currently looking for more sources of catfish. The most obvious being local lakes. So now I have a great motivation for picking up a fishing license and learning how to fish!