Why You Should Use a Bell Siphon for Aquaponics

The mechanical function, installation, benefits, and troubleshooting guide to a bell siphon for aquaponics, as well as where to buy a great one.

Updated: November 22, 2023
Jeremiah Zac


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Those who are familiar with the mechanics of an aquaponics system understand the importance of the continuous rising and falling of the water levels.

This ebb and flow allows vital nutrients to be distributed throughout the entirety of the system, ensuring a healthy, functioning environment.

While electric-powered water pumps are a common and convenient way to enforce proper water circulation, they are not without their own disadvantages.

Accrued electric costs and the occasional malfunction are familiar realities of water pump users.

The bell siphon is a simple, physics-driven device that automates water flow in an aquaponics system without the need for electrical power.

With some precise calculating and the help of gravity, a bell siphon can completely automate the water cycle in an aquaponics system.

In this article, we'll cover:

  • The importance of a bell siphon for aquaponics systems
  • The components of a bell siphon and how to install one
  • Troubleshooting common problems with bell siphons
  • Where can I purchase a good-quality bell siphon for my aquaponics system?

Well-constructed PVC Bell Siphon

  • Made in USA
  • Well-reviewed by Aquaponics Farmers

Smoky Mountain Aquaponics manufactures bell siphons for 4.5", 6", 8", 10", and 12" media beds. Trusted by aquaponics professionals and enthusiasts alike, these bells siphons are a reliable choice for you system.

Check latest price

Bell Siphon 6 inch

What is a Bell Siphon?

A Bell Siphon is a simple device used to regulate the flow of water in aquaponic and hydroponic systems easily and efficiently, with no need for human intervention.

The siphon first allows the grow bed to flood and automatically drains out the water when it reaches a certain level. The siphon also maintains a minimum water level as the excess water is drained.

Bell siphons avoid the need to manually turn the pump on and off during the flood and drain cycle. The flood and drain cycle is implemented to boost oxygenation and help the plants absorb more nutrients. Thus, the cycle plays a crucial role in ensuring the healthy growth and development of plants.

How Does a Bell Siphon Work?

Bell siphons implement a very simple mechanism which leverages the forces of pressure and gravity.

bell siphon

  1. The drained grow bed is first filled with water using a water pump.

  2. When the water level reaches the top of the standpipe inside the siphon pipe, water will start flowing through the reducer placed at the top and out through the standpipe into the fish tank at a low pressure.

  3. As water slowly drains out of the standpipe, water builds up inside the bell and pushes air out through the standpipe. As a result, the pressure inside the bell eventually falls.

  4. The resulting low pressure in the bell leads to a pressure difference between the bell and the atmosphere, which forces the siphon to fire. Thus, the siphon rapidly pushes out and dumps the water through the standpipe at a much higher pressure until the water level reaches the base of the grow bed.

  5. As the water level approaches the base of the siphon pipe, air enters the bell through the slits at the bottom of the siphon pipe, relieving the pressure difference between the bell and the atmosphere, causing the siphon to break and halt the water drain.

As the pump continues to run, water will keep pouring into the grow bed. Once the water level reaches the top of the stand pipe, the siphon is triggered again. This flood and drain cycle repeats indefinitely until the pump is stopped.

How is a Bell Siphon Beneficial for an Aquaponics System?


In aquaponic systems, bell siphons allow water from the grow bed to be automatically drained into the fish tank and the pump to take water from the fish tank into the grow bed. In addition to the automatic regulation of water, which greatly saves the time and effort of aquaponic farmers, bell siphons have several other benefits when used with aquaponic systems.

More Aeration for the Plants’ Roots

Using a bell siphon improves the oxygenation of the plants. As the bell siphon drains out the water regularly, the full lengths of the roots are exposed to air regularly. This promotes oxygen intake, thus aiding in plant growth and the overall health of the plants. The indefinite flood and drain cycle allows the plants to remain hydrated and take in nutrients and oxygen for a balanced intake of required elements.

Constant and Consistent Movement of Water

Bell siphons allow for the constant and consistent movement of water out of and into the grow bed. This regular in-and-out flow of water improves the oxygen level of the water and prevents water stagnation which could attract bacteria, mold, mosquitoes, and rodents. The water flow improves support for the healthy growth of the plants.

The Process is Automatic

Bell siphons work automatically with the support of Physics concepts. This makes the process very efficient for the farmers. You would not need to manually drain the grow bed, which saves a tremendous amount of time. There is no need for a timer and other additional drainage equipment, which also helps save costs.

Ensures Maximum Efficiency

Bell siphons enable your aquaponic system to function at maximum efficiency as the process takes place automatically. After trial and error, once you establish the optimum water pump flow rate, the bell siphon maintains a consistent flood and drain cycle at regular intervals.

Simple and Reliable

Bell siphons are relatively easy to maintain. All you need to do is a little routine cleaning once in a while and some troubleshooting after installing. Bell siphons are also very easy to set up, and they require no electricity.

Bell Siphon Components

Bell siphon

A bell siphon consists of 7 main components

Bell Cap

The bell cap plays a crucial role. As water overflows into the standpipe, low pressure eventually builds under the bell cap, which ends up forcing out water at a higher rate until air enters the bell when the water level reaches the slits at the base of the siphon pipe.


The reducer is placed at the top of the standpipe, which helps to create the siphon in the discharge pipe with a smooth transition. A reducer with a 2:1 ratio has proved to be the optimum – if the standpipe is 1 inch in diameter, a reducer with a diameter of 2 inches at the top and 1 inch at the bottom will be most suitable.

Siphon Pipe

The siphon pipe creates a barrier between the siphon and the atmosphere, preventing air from entering inside. It allows the siphon to build up a negative pressure which then creates a vacuum that keeps water flowing in the siphon. The siphon pipe usually has slits at the bottom to allow air into the system once the grow bed drains to stop the siphon with the rise of pressure.

A good rule of thumb – the siphon pipe should have a diameter twice as big as the reducer.


The standpipe is placed inside the siphon pipe and acts as the discharge pipe, regulating the maximum water level in the grow bed. It connects the bulkhead to the reducer. The water flows out through the standpipe once it reaches the top of the standpipe.

Media Guard

The media guard acts to keep rocks and other debris off the siphon pipe while allowing water to easily flow in and through the standpipe. The guard prevents the support medium used in the grow bed from clogging the standpipe and bell siphon.


The bulkhead allows water to drain through the standpipe without leaking back into the siphon. It also holds the stand pipe in the grow bed.

Outlet Pipe

The outlet pipe, or drain pipe, extends from the bottom of the bulkhead into the fish tank.

Video: Bell Siphon Animation

Watch this short animation explaining how a bell siphon works.

Set Up and Installation

bed-diagram aquaponics

Follow the below steps to install your bell siphon.

Step 1 – Prepare the Ground with Your Tiles

Stack the tiles to your preferred height, then place the table on which you are hoping to keep the grow bed on top of the tiles. Make sure that the table and tiles are leveled out to ensure that your table is stable. Also, remember to leave enough space for your fish tank if you are hoping to place the tank underneath the table.

Step 2 – Place your Grow Bed

Place your grow bed on the table and check to make sure that the bed is leveled and stable.

Step 3 – Set up your Bell Siphon

  1. Put the uniseal in the hole at the bottom of the grow bed, then place the standpipe

  2. Push the standpipe through the top of the uniseal until the top of the standpipe is at the height of the bottom on the bell cap on the bell siphon.

  3. Connect the rest of the drain leading to the fish tank by fixing the 90-degree elbow onto the bottom part of the standpipe sticking out below the grow bed

  4. Position your gravel guard around the standpipe with the pipe at the center, then weigh down the guard with a bag of cinder

Step 4 – Fill Up your Grow Bed

Using cinders, fill up the rest of your grow bed to the height of the top part of the standpipe. To check if the cinders are high enough, you can fill the grow bed with water to the top of the standpipe using a hose. This will expose low spots in the form of puddles. If there are any puddles, you can add cinders to level out the low spots. The goal is to make sure that you are unable to see the water level when it is at the top of the standpipe – the cinders should prevent you from seeing the water level.

Step 5 – Rinse your Cinders

When you handle the cinders, there will be some black particulate. To rinse them, place the bell siphon over the standpipe, then continuously shoot the cinders placed in the grow bed from the top with a water hose. Let the water drain out via the bell siphon. You can stop shooting the water once you feel that the cinders are clean.

Make sure that the rinse water is not draining into the fish tank!

Step 6 – Complete the setup

  1. Place the fish tank underneath the grow bed and fill up the tank with water once you have ensured that the grow bed has completely siphoned all the rinse water.

  2. Place the pump and piping in the fish tank and zip-tie the piping to the lip of the grow bed for stability

  3. Turn on the pump and make sure that the siphon is working properly

  4. Add your fish and vegetables. You may add the organic digester to the fish tank before adding the fish.

Additional tips:
  • Ensure that the standpipe is not too tilted, as it can slow down the drain system

  • Set up the bell siphon unit at the center of the grow bed, the best place possible


Here is a brief outline of how to deal with the two most common issues faced with bell siphons.


The bell siphon will not trigger – the water level in the grow bed stays high and may overflow, but the water doesn’t flush

Possible solutions:

  1. Check the seal connecting the cap to the siphon pipe. The seal needs to be airtight; if not, the vacuum needed to initiate the siphon action will not form

  2. Make sure that the bell siphon and gravel guard are firmly placed at the bottom of the grow bed. If not firmly in place, pieces of cider may move under the siphon pipe, which will create extra space between the bell and the standpipe. This additional space can prevent the siphon from triggering.

  3. Increase the flow of water entering the grow bed to trigger the bell siphon

  4. Increase the resistance of the drain pipe where water returns to the fish tank by turning the 90-degree elbow up so that the water can build up and then dump


The bell siphon dumped the water, but the grow bed is not filling up again – the water in the grow bed remains at a low level and keeps flowing out of the drain pipe.

Possible Solutions:

  1. Adjust the incoming flow rate by decreasing the flow of water entering the grow bed to allow the bell siphon to suck up air to break the seal. The siphon will find it difficult to drain the grow bed if the rate of water flow is too great

  2. Adjust the drain by decreasing the resistance of the drain pipe by turning the 90-degree elbow down to let the water drain faster and allow the siphon to take in air. A slightly longer or shorter vertical or horizontal drainpipe may also fix the problem.

Remember to make sure that the drain pipe is not too long, as it will create more resistance which will, in turn, affect the siphon.

What are the Best Bell Siphon Kits I Can Buy?

Smoky Mountain Aquaponics manufactures an excellent bell siphon constructed from various sizes of PVC pipe. Accommodating media sizes of 4.5", 6", 8", 10" and 12", these Bell Siphons are well-constructed and highly reviewed by Aquaponics farmers around the world. Having sold over 7000 siphons worldwide, Smoky Mountain Aquaponics is quickly becoming a trusted brand in Bell Siphon manufacturing. All gravel shields are slotted for maximum drain and maximum filtering. No-clog bell comes with cap and pull handle and is easy to assemble and install.

  • Media size: 4.5"
  • 2" x 5" Slotted PVC Gravel Shield
  • 1.25" x 4" PVC Bell

Bell Siphon 4 1:2

  • Media size: 6"
  • 2" x 7" Slotted PVC Gravel Shield
  • 1.25" x 6.5" PVC Bell

Bell Siphon 6 inch

  • Media size: 8"
  • 3" x 9" Slotted PVC Gravel Shield
  • 2" x 6.5" PVC Bell

Bell Siphon 8 inch

  • Media size: 10"
  • 4" x 12" Slotted PVC Gravel Shield
  • 3" x 10" PVC Bell

Bell Siphon 10 inch

  • Media size: 12"
  • 4" x 14" Slotted PVC Gravel Shield
  • 3" x 12" PVC Bell

Bell Siphon 12inch


If the water pump is considered the heart of an aquaponics system, pumping nutrient-rich water to all the necessary parts, the bell siphon might be considered the lung. It uses air pressure to regulate a steady rise and fall in the water level. A well-constructed bell siphon will keep an entire system flowing properly, simply by physics.

Thank you for taking the time to read our article on the bell siphon for aquaponics. We'd love to hear your feedback in the comments section below. If you've found this article to be useful and are interested in learning more, be sure to sign up for our newsletter.

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I'm Jeremiah, the owner of World Water Reserve. I'm a writer and researcher with a particular interest in sustainability and rural living, water scarcity, and innovative water purification methods. I utilize my multimedia and communication experience in the NGO and humanitarian fields to bring light to important topics. My passion is to educate others on the reality of the global water crisis and on ways to sustain themselves and their families in the midst of it.
Jeremiah Zac