Bell Siphon in Aquaponics

The Importance of Bell Siphon in Aquaponics Systems

A bell siphon is another component of a media based aquaponics system that regulates the water flow. It also efficiently helps move the water in your media bed aquaponics system. If you’re planning on building your own media based aquaponics system, it is necessary that you understand the importance of a bell siphon. This article explains what a bell siphon is and its significance in a media based system

What is A Bell Siphon?

A bell siphon is a device used to regulate and control the water levels in your grow bed automatically without human intervention. It maintains the minimum water level in the grow bed and drains the excess water. The bell siphon also automatically allows the water to flood the grow bed and drains it when it reaches a certain level. The bell siphon maintains a minimum water level in the grow bed, so it never dries out. Bell siphons do not require manual triggers or moving parts to function.

Bell Siphon in Aquaponics

When to Use A Bell Siphon in Aquaponics

Flood and drain use bell siphons as an automatic machine to flood and drain the grow bed. The draining of the water allows plants to have a dry cycle and be exposed to air. A bell siphon enables aquaponics growers to control the water level in the grow bed, distributing water in the entire system. 

Benefits of using a bell siphon

  1. As the bell siphon drains out the water regularly, the plants’ roots are exposed to air regularly, allowing the plants’ roots to remain hydrated and absorb all the nutrients in the water and the air that is beneficial for the overall health of the plants.
  2. The bell siphon allows the water’s constant and consistent movement, which improves oxygen in the water and prevents the water’s stagnation.
  3. The bell siphon process works automatically. Once the bell siphon is working, you don’t need a timer, additional drainage equipment, or manual draining to use the bell siphon in your system. The continuous cycle prevents extra work on your part.
  4. Bell siphons are easy to maintain and simple to use.
  5. Bell siphons are also easy to set up and require no electricity to function, which enables your aquaponic system to work efficiently.

How Does A Bell Siphon Work?

Bell siphons use a mechanism that leverages the forces of pressure and gravity. As your grow bed fills up with water and reaches the top of the standpipe located inside the siphon pipe. The water will flow through the reduced pipe placed at the top of the standpipe and through the standpipe into the fish tank at low pressure.

As water drains slowly out of the standpipe, the water builds up inside the bell and pushes air out through the standpipe. The pressure inside the bell falls as a result. The resulting low pressure in the bell will lead to a pressure difference between the bell and the atmosphere, making the siphon fire. The siphon pushes out and dumps the water rapidly through the standpipe at a higher pressure until the water level reaches the grow bed base.

As the water level approaches the siphon pipe base, air will enter the bell through the holes at the bottom of the siphon pipe and relieve the pressure difference between the bell and the atmosphere, which causes the siphon to break and halt the drain of the water.

As the pump continues to pump, the water will keep pouring into the grow bed, and once the level reaches the top of the standpipe, the siphon will be triggered again, and the flood and drain cycle will repeat until the pump is stopped.

Bell Siphon Size

One of the questions in using a bell siphon is, what size will you use? The rule of thumb is, your main siphon components should be equal to or slightly greater than the water inflow components.  

Just think, if you have a high volume of water entering your grow bed through a 40 mm pipe, but your standpipe and outflow are only 20 mm. Your 20 mm could not cope with the volume of water, and your grow bed would overflow. But if you reverse the situation and use the 40 mm outflow, it will easily handle the amount of water that the 20 mm pipe could put into your grow bed. Your grow bed will not overflow. 

So it is essential to consider the amount of water flowing to your grow bed, your pump capacity and how fast the water will flow, how many flood and drain cycles you will need to do in an hour in choosing the size of your bell siphon.

media based aquaponics system

Components of a Bell Siphon

If you want to build your own bell siphon, it is easy to understand each component because there are only a few parts of a bell siphon. The components of a bell siphon are simple and available at most local hardware stores. The media guard can be drilled or cut, depending on your preference. These are the components of a bell siphon.

1. Bell Cap

As the water overflows into the standpipe, low pressure will eventually build up under the bell cap. Forcing the water out faster until air enters the bell when the water level exceeds the slits at the base of the siphon pipe. 

2. Reducer

This is placed on top of the standpipe, which helps the siphon discharge pipe create a smooth transition; a 2:1 ratio in a reducer is optimum. (if the standpipe is 1 inch in diameter, a reducer should be 2 inches).

3. Siphon Pipe

The siphon pipe should be twice as big as the reducer. Bell siphon pipe creates a barrier between the siphon and the atmosphere and prevents air from entering inside. It also allows the siphon to build up a negative pressure that creates a vacuum that keeps the water flowing in the siphon.

4. Stand Pipe

This is placed inside the siphon pipe and the discharge pipe. Standpipe also regulates the maximum water level in the grow bed. Water flows out through the standpipe once it reaches the top of the standpipe. It also connects the bulkhead to the reducer.

5. Media Guard

The media guard prevents the growing media in the grow bed from clogging the standpipe and bell siphon.

6. Bulkhead

Bulkhead holds the standpipe in the grow bed and allows the water to drain through the standpipe without leaking back to the siphon.

7. Outlet Pipe

Also called a drainpipe, this extends from the bottom of the bulkhead into the fish tank. 


Putting The Bell Siphon Together

  1. First, drill a hole in your grow bed, put an uniseal in the hole, and then place the standpipe. Ensure that you have the correct size drill bit for the PVC fittings (bulkhead) you are using.
  2. Push the standpipe through the uniseal’s top until the standpipe’s top is at the height of the bottom of the bell cap.
  3. Connect the drain leading to the fish tank by using a 90-degree elbow into the bottom part of the standpipe below the grow bed.
  4. Position your grow media around the standpipe. Fill up your grow bed with grow media to the height of the top part of the standpipe. To check if your grow media are high enough, fill your grow bed with water to expose low spots.
  5. Place the fish tank under your grow bed and fill up the tank with water once you have ensured that your grow bed has siphoned all the rinse water.
  6. Place the pump and pipes in the fish tank. Make sure it is stable.
  7. Turn on the pump to make sure your siphon works properly.
  8. Once you have completed the setup and cycled your system, you can start adding your fish and planting your crops.


Using a bell siphon in your media-based aquaponics system is an excellent way to ensure that your system runs smoothly without any mechanical intervention. A bell siphon works automatically and keeps the water in your system moving efficiently. Making and installing your own bell siphon is not difficult if you know its functions and components.