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Scaling Up to a Larger Aquaponics System – Part 3

Previously in Part 1 of Scaling Up to a Larger Aquaponics System, I talked about how the aquaponics system was put together. In Part 2, I covered startup and operation. Here in part 3 of this 4 part series, I will review the results and some adjustments I made.

Results
Initially the plants didn’t seem to do much. It is normal for young plants to put all their early energy into developing their roots, and oh boy were these plants developing roots! The access to water and oxygen in the aquaponics system results in tremendous root growth. After a few weeks the visible growth on top started. The growth was phenomenal. It wasn’t long before the squash leaves were massive. The sesame and pepper plants did very well too. You would never plant vegetables in soil this densely, but they did fine in the grow beds. This is because the nutrient rich water is constantly circulating, making the nutrients readily available to all of the plants.

New Sesame Plants in the Grow Beds

New Sesame Plants in the Grow Beds


Sesame Plants After 3 Weeks

Sesame Plants After 3 Weeks


Sesame Plants After 4 Weeks

Sesame Plants After 4 Weeks


The Roots of a Sesame Plant

The Roots of a Sesame Plant

One thing I learned was that the fruiting vegetables had great green growth, but fruit production was weak. This is due to the high nitrogen levels in the nitrates which promote green growth. Fruit production needs phosphorous which is not naturally abundant in an aquaponics system, so it must be added. The problem is that phosphorous will cause leafy plants like lettuces to go to seed. Rather than having separate systems, I used a product called rock phosphate. It comes in the form of small rocks that can be placed right around the base of each plant. The rocks release phosphorous slowly directly to the roots, minimizing the overall levels in the water. I felt like I saw some improvement in fruit production with the addition of the rock phosphate but not a huge difference.

Yellow Squash After 5 Weeks

Yellow Squash After 5 Weeks


After 7 Weeks

After 7 Weeks

While the squash plants had giant green leaves, fruit production was only average. The same can be said for the cucumbers. Since the sesame plant produces edible leaves, I would call this one a success. The leaves can be cooked like spinach or stir fried. One plant that did especially well were banana peppers. The plant had good growth, but the output of peppers was extremely high. I would estimate that each plant produced 30-40 peppers. I’m not sure if this was because the rock phosphate worked or it they plants simply like the high nitrogen environment. All I know is I had so many peppers I was giving them away!

Peppers

Peppers

As the cucumbers grew, I added vertical supports and wires so they could climb away from the system. This took advantage of the nutrient dense water for the roots, but vertical growth makes efficient use of real estate.

Cucumbers and Squash

Cucumbers and Squash

All in all I thought the plants did very well. The system seems to be best suited for leafy green plants. In later posts, I’ll talk about how I made modifications to the system to focus more on lettuces.

All the Beds After 5 Weeks

All the Beds After 5 Weeks

Harvesting Fish
The cool thing about aquaponics is that you get more than just plants. You can also get protein through harvesting the fish. I wanted the fish to grow as big as possible, so I waited late in the fall as possible. When the outside temperature dropped in October, the water temperature in the tank also started dropping. Tilapia can live down to about 50F.

When the temperature got down in the 50s, the fish began to get sluggish and stop eating. It was time to harvest the fish. I netted the fish out of the tank a few at a time for processing. I filleted the fish, vacuum sealed them, and put them in the freezer. The remains went in the black soldier fly larvae bin for composting.

Filleting fish is hard work. I made sure I had some good gloves and a fillet knife. I had a lot of them to do. So I called a friend to help me out. In exchange, he took several pounds of fish home with him. If the system were heated or located where the temperature wouldn’t drop, you could only harvest what you need to use and let the rest keep growing. That would be a more productive setup. I didn’t have that luxury with this system.

The tilapia were a decent size but not what I would call full size. Trying to grow them to maturity in only 8-9 months had its limitations. Still I got about 15 pounds of fillets from 50 fish which wasn’t too bad.

Making Adjustments
I checked the system daily for proper operation. I also did daily water tests to monitor the nitrate levels. For the next couple weeks, my focus was on balancing the water flows so the bell siphons worked properly.

As I discussed in part 1, I use two pumps for redundancy. This also creates an excess water flow into the fish tank, resulting in a constant flow of water back to the sump tank through the overflow line. The fish tank level remains constant at the height of the overflow line. The constant height means a predictable pressure in the discharge line to the grow beds, making it easier to control the flow rates into the beds. If the water level in the fish tank varied, so would the pressure, requiring constant tweaking of the valve positions. If the flow is too high, the drain cycle will never break and begin flooding again. If the flow is too low, the siphon won’t start and the bed stays flooded. I try to error on the side of a lower flow. I would rather come home from a day at work to find the bed flooded than drained. The plants can handle their roots sitting in water too long a lot better than drying out on a hot Georgia day. So my approach was to try to find the flow rate where the siphon seems to barely start, and tweak it up slightly from there.

Another adjustment I had to make on the fly was due to the extreme heat we sometimes get here in the summer. I had acquired a submersible temperature sensor to monitor the water temperature. As the days got hotter, I noticed the water temperature in fish tank going through some fairly significant fluctuations between night and day. Sometimes it varied as much as 25 degrees F which must have been stressing the fish. To smooth this out, I constructed what amounted to an insulating box around the tank made up of ½” foam panels reinforced with 1”x4” boards. I built the top with hinges so one half of it could be opened for feeding and other maintenance. The result was to keep heat in at night but even more important was to prevent overheating during the day. After this improvement, the temperature fluctuations were 10 degrees or less.

Insulating Enclosure Around the Fish Tank

Insulating Enclosure Around the Fish Tank

There were other adjustments I had to make along the way. When the plant growth got vigorous, I would sometimes get roots growing into the bell siphon sleeves which can impact the operation. I would simply pull the bell out and clean the roots up with a pair of scissors.

There were a few minor leaks in the PVC pipe joints. While I started out with all joints just tightly pressed together, I had to glue the joints in the area from the tank discharge bulkhead fitting to the first grow bed valve since this area was always under more pressure. Another time I had to tighten the bulkhead fitting. Leaks cause loss of water so you have to keep an eye out for them. When you see the sump tank level dropping too low, it’s time to check for leaks.

There is also always some water loss due to evaporation. I was pleasantly surprised how little water had to be added to the simply routinely but it is necessary. Typically I would add no more than 5 gallons a week which isn’t bad for a system with over 300 gallons.

What’s Next?
Join me next time for the final part of this 4 part series. I’ll discuss some additions I made and my overall conclusions about the year long experimental system.

Resources for this post:
Introduction to Aquaponics
My First System: A Small Scale Aquaponics System
Building the larger system: Part 1 of Scaling Up to a Larger Aquaponics System
Startup and Operation: Part 2 of Scaling Up to a Larger Aquaponics System

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