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Scaling Up to a Larger Aquaponics System – Part 1

Previously I talked about the small-scale aquaponics system I built a few years ago. You can read about it here: A Small Scale Aquaponics System. I was happy enough with the results that I decided to try a bigger system. I wanted to scale it up to see if I could get some significant production from it. The system required the same components as the smaller one – grow beds, a fish tank, and a sump tank – but they would all need to be bigger than before. In this multi-part series, I’ll cover the components first, then startup, operation, and results.

Aquaponics Systems - Fish Tank at the Far End

Aquaponics Systems – Fish Tank at the Far End

Fish Tank

For the fish tank, I decided to use a 330 gallons IBC tote. This one came from the same source as my water tanks. The tank sits on a concrete pad I happened to already have. Otherwise, you need to set it on something level and strong like concrete blocks. I cut the top off of the plastic tank, keeping the metal support frame intact, and thoroughly washed the inside.

Grow Beds
The grow beds are made from 55 gallons plastic drums I got from a local salvage store for $10 each. They were food grade and had originally been used to store vinegar. Three of the barrels were cut in half lengthwise using a jigsaw to form six 3’x2’ grow beds. The supports for the grow beds are made up of concrete blocks and some lumber.

I built the bases by stack concrete blocks to form two rows of piers. It is important to make the tops of them all level so the resulting grow beds will be level. The two rows of piers were spaced so that they would be near each end of the barrels. The height of the piers depends on your exact design. You’ll want to think through this and plan it all out before building. My design uses a gravity feed so the grow beds had to be below the fish tank discharge line. This determined the height of the piers.

Concrete Supports and 4"x4" Horizontal Supports

Concrete Supports and 4″x4″ Horizontal Supports

Grow Bed Supports

Grow Bed Supports

A single piece of pressure-treated 4”x4” was laid across each row of piers. The result is two parallel 4”x4”s that provide support for a series of 2”x6”s and 2”x4”s that support the barrels. Every barrel gets a set of supports on each side. A support is made up of a 2”x6” at about a 45 degree angle supported by a 2”x4”.

Construction of the Grow Beds in Progress

Construction of the Grow Beds in Progress

Once the barrels are filled with grow media, the sides need support to prevent them from flattening out under the weight. That’s a problem since the grow beds have to hold water. You can see in the picture how they are supported. The six grow beds are lines up side by side in a line.

Grow Beds

Grow Beds

Sump Tank
The sump tank is also a 55 gallon plastic drum. I cut the top off with the jigsaw. The cut is inside the top ring which gives the drum strength. Since my system is gravity fed, the sump tank needed to be below the discharge of my grow beds. My system is built on a slight downhill slope but I still had to dig a hole to set the sump tank into the ground a few inches. This was much easier than raising fish tank and grow beds higher. With the sump tank in place, you can see in the picture that everything is in a line. This certainly isn’t necessary but it fit my space best.

Overall Design
With all of the basic components in place, it was time to put together the plumbing. As I described before, the concept is straightforward but there is more than one way to do it. Water needs to be pumped out of the bottom of the fish tank so it picks up the settled waste. It flows into the grow beds which flood and drain. When the grow bed drains, the water flows into the sump tank. Then the water must get back to the fish tank. Because the sump tank is at the low point of my system, a submersible pond pump in my sump tank pumps the water back up to the fish tank.

I wanted the fish tank water level to stay constant for two reasons. First, I didn’t want an environment that might shock the fish and I thought a constantly changing water level might do that. Second, and more importantly, the water level affects the flow rates because it is a gravity feed system. I’ll explain more about that in a minute. Since I wanted the fish tank level to remain constant, the sump tank acts as the buffer. Its level fluctuates up and down during the flood and drain cycles.

Plumbing
Water is pumped continuously from the sump tank to the fish tank. I use two pond pumps for redundancy just in case one of them fails. Each pump is plumbed with a short garden hose to a 1” PVC pipe which is routed to the fish tank. I use 1” thin-walled PVC which allows a higher flow rate. The system operates under low pressure so heavier PVC is not needed. The water is sprayed out of pipes with holes drilled in them so create aeration on the surface of the fish tank. The pumps are sized so there is more flow than necessary to prevent the tank level from dropping. This will make more sense in a minute.

The discharge line from the tank is a larger 2” PVC pipe. It is about 12” below the water level of the tank. The height difference creates pressure in the lines necessary to keep the flow rate where I want it. To create a water tight connection to the tank, I used an aquarium bulkhead fitting. The discharge line runs inside the tank to a pickup at the bottom of the tank so it gets the nutrients that settle to the bottom. The end of the pickup is covered by wire and window screen to prevent it from picking up debris or fish. The discharge line runs downhill to the grow beds where a series of tees and valves allow me to adjust the flow rate into each grow bed.

Pickup Line Inside Fish Tank

Pickup Line Inside Fish Tank


Discharge Line from Fish Tank

Discharge Line from Fish Tank

To control the level of the tank, I installed another 2” PVC line with a bulkhead fitting at the desired level which runs directly back to the sump tank which I call the overflow line. This allows the excess flow into the fish tank from the two pumps to run directly back to the sump. The opening to the overflow has a screen over it so fish can’t get out of the tank. As long as the flow rate into the tank is higher than the flow rate out, the overflow line will keep the fish tank level constant. The constant level results in a consistent pressure on the discharge line, making it easier to adjust and maintain the flow rates to the individual grow beds. Predictable flow rates are necessary to get the bell siphons to work correctly.

Each grow bed has two ways water can get out. First, the bell siphon that controls the flood and drain cycle. You can read more about bell siphons in my earlier posts and on the internet. Basically, it is made up of three components – a standpipe attached to the bottom of the bed, a larger bell which is placed over the stand pipe, and a protective sleeve that goes around the bell. The protective sleeve has holes or slots to allow water to flow in so the bell siphon can function. Its main function is to prevent grow media from getting in and interfering with the operation of the bell siphon.

The standpipe attaches to a pipe under the grow bed which sends the discharge into a large 4” PVC pipe that carries it to the sump tank. All six grow beds discharge into the same 4” pipe. A hole is cut in the top of the 4” pipe for each discharge line. The 4” pipe is mounted with a slight downhill slope toward the sump tank. It basically acts like a gutter to carry the water from all the grow beds to the sump tank. You might wonder why I didn’t just use a gutter. It was because the discharge can be very rapid when the siphon starts, and a lot of water could splash out. The 4” PVC pipe prevents that. Water loss in this system could cause the sump tank to eventually run dry resulting in system failure. Everything is designed to avoid water loss.

Grow Bed Plumbing

Grow Bed Plumbing

The 2nd exit from the grow bed is an overflow line installed in the side of the bed at the desired level to avoid the bed overflowing out the edges. This is only there in case the bell siphon fails to start or clogs. These overflow lines from the six beds are all tied together and run downhill to the sump tank.

Finally a note about the PVC plumbing. I only glued a few of the joints, mainly the most critical ones around the discharge from the fish tank. Most of the fittings are just stuck together. I wrap duct tape around them to give a little reinforcement to hold them in place. Because the system is gravity fed, the pipes are not under pressure. By not gluing the fittings, I have been able to make adjustments along the way very easily. If the fittings were glued, adjustments would more likely require redoing the plumbing for a larger section.

What’s Next?
Join me next time for part 2 when I’ll cover the startup and operation of the system. We’ll add fish and plants, and you’ll see that some of the results were surprising.

Resources for this post:
Introduction to Aquaponics
A Small Scale Aquaponics System

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