What is a Bell Siphon and Why We Use it in Aquaponics

 

One of the most crucial components of a well-functioning aquaponics system is the bell siphon, a simple yet powerful device that automates water flow in a flood and drain grow bed system. Without a properly functioning bell siphon, maintaining an optimal balance of water, nutrients, and oxygen for plant roots becomes a challenge.

In this guide, we’ll dive deep into how bell siphons work, why they’re essential for aquaponics water management, and how to build and troubleshoot your own DIY bell siphon. By the end of this guide, you’ll have a clear understanding of how to install, maintain, and optimize a bell siphon to ensure healthy plant growth and efficient water circulation in your aquaponics system. 

What Is a Bell Siphon and Why Is It Important in Aquaponics?

A bell siphon is a passive, automatic draining mechanism that controls the water level in a media based or flood and drain aquaponics system. It allows the grow bed to fill with nutrient-rich water before quickly draining it, ensuring that plant roots receive both water and oxygen in the right proportions. This flood and drain process mimics natural conditions, promotes healthier plant growth while preventing issues like root rot and stagnant water buildup.

Why a Bell Siphon Is Essential for Media Based Systems

In a media based aquaponics system (also known as flood and drain system), maintaining the correct water cycle is crucial for plant health. A bell siphon replaces the need for complex timers and electrical pumps by:

1. Ensure consistent water flow:Automates the draining of the grow bed without manual intervention.
2. Prevents overwatering and root rot: Allows plants to absorb nutrients before draining excess water.
3. Increase oxygen supply: As water drains, oxygen reaches the plant roots, improving nutrient uptake and growth.
4. Reducing energy consumption:Functions without electricity, making it a cost-effective solution for aquaponics.

 

How Does a Bell Siphon Work?

A bell siphon operates entirely on gravity and water pressure and eliminates the need for sensors or mechanical controls. The siphoning process follows a simple cycle:

1. Water fills the grow bed:Water enters from the fish tank, gradually rising to the set maximum level.
2. Siphon activation:Once the water reaches the top of the standpipe, it triggers the vacuum effect, rapidly draining the bed.
3. Complete draining phase: The siphon continues to remove water until the grow bed is nearly empty.
4. Break and reset:Air enters the siphon, breaking the vacuum, and the cycle begins again.

This automated process ensures that plants receive periodic flooding for nutrient absorption while preventing excess water stagnation, making bell siphons an indispensable tool in aquaponics.

Components of a Bell Siphon 

A bell siphon consists of three main parts, each playing a critical role in ensuring efficient water drainage in an aquaponics system.

1. Standpipe: Controls the Water Flow Rate

• The standpipe is the vertical pipe that determines the maximum water level in the grow bed.
• Water flows over the standpipe when it reaches the top, initiating the siphon effect.
• The diameter of the standpipe influences the drainage speed, wider pipes drain water faster.

2. Bell Dome: Creates the Vacuum Effect

• The bell dome is a larger pipe that covers the standpipe, creating an airtight chamber.
• As water flows over the standpipe, the dome traps air, forming a vacuum effect that accelerates the drainage.
• Once the grow bed is nearly empty, the vacuum breaks, stopping the siphon.

3. Gravel Guard: Prevents Clogging from Aquaponics Grow Media

• The gravel guard is a perforated cover that surrounds the bell siphon to keep solid debris, roots, and grow media from clogging the system.
• It ensures uninterrupted water flow, preventing blockages that could disrupt the siphoning process.

A Step-by-Step Process on How a Bell Siphon Works

A bell siphon operates in a four-phase cycle, ensuring automatic flooding and draining without the need for pumps or timers.

1. Water Fills the Grow Bed: The Siphon Remains Inactive

• Water from the fish tank is pumped into the grow bed.
• As the water level rises, it approaches the top of the standpipe.
• The bell siphon remains inactive at this stage.

2. Triggering the Siphon Cycle:  The Bell Siphon Starts Draining the Water

• When the water level reaches the top of the standpipe, it begins to overflow into the pipe.
• This creates a suction effect, pulling water rapidly through the bell dome.
• The vacuum effect is established, accelerating water drainage.

3. Draining Phase:  Water Exits Completely, Delivering Oxygen to Plant Roots

• The siphon continues to drain the grow bed until most of the water has been removed.
• As water drains, oxygen is pulled into the grow bed, preventing anaerobic conditions and root rot.
• This ensures healthy plant growth and improved nutrient absorption.

4. Break Phase: The Siphon Stops, and the Grow Bed Starts Filling Again

• As the water level drops, air enters through the bottom of the bell dome, breaking the vacuum effect.
• The siphon stops draining once enough air enters the system.
• Water starts filling the grow bed again, and the cycle repeats automatically.

Why Use a Bell Siphon in an Aquaponics System?

A bell siphon is one of the most efficient and low-maintenance drainage solutions for a media based system. Unlike traditional methods that rely on electrical timers and pumps, a bell siphon automates the draining process naturally, ensuring an optimal balance of water, nutrients, and oxygen for plant growth.

Benefits of a Bell Siphon in Media Based Aquaponics Systems

A media based or flood and drain system relies on periodic flooding of the grow bed, followed by complete drainage to supply nutrients while preventing water stagnation. A bell siphon provides the ideal solution for this process by automating the water cycle without requiring external controls.

1. Automatic Water Regulation: No Need for Electrical Pumps:

One of the biggest advantages of a bell siphon is that it regulates water flow automatically without requiring electrical timers or sensors. It ensures that:

• The grow bed fills to the correct water level before draining.
• The drainage process is triggered without human intervention.
• The cycle repeats consistently, providing plants with a steady supply of nutrients and oxygen.

By removing the need for electric-powered controls, a bell siphon reduces system complexity and long-term maintenance.

2. Prevents Root Rot by Ensuring Proper Drainage:

One of the biggest challenges in aquaponics is preventing overwatering, which can lead to root rot and fungal diseases. A bell siphon helps by:

• Ensuring the grow bed never remains flooded for too long.
• Allowing excess water to drain quickly, preventing water stagnation.
• Keeping plant roots moist but not submerged, promoting healthier growth.

Proper drainage is essential for a thriving aquaponics system, and a bell siphon provides consistent and efficient water management.

3. Increases Oxygenation for Healthier Plant Growth:

Plants need oxygen just as much as they need water. A bell siphon promotes oxygenation by:

• Creating a dry period after each drainage cycle, allowing plant roots to absorb oxygen.
• Preventing anaerobic conditions that can lead to stunted plant growth.
• Encouraging stronger root development, leading to higher yields and healthier crops.

With a properly functioning bell siphon, plants receive regular oxygen boosts, improving overall nutrient uptake and growth efficiency.

4. Energy-Efficient Solution for Aquaponics Irrigation:

A bell siphon operates entirely on water pressure and gravity, making it a 100% energy-efficient solution.

• No electricity required: Saves on energy costs.
• Lower long-term maintenance: No need to replace timers or electronic parts.
• Reliable in off-grid setups: Ideal for sustainable and eco-friendly aquaponics systems.

By using a bell siphon, aquaponics growers can enjoy a low-cost, high-efficiency system with minimal operational costs.

How to Build a Bell Siphon for Aquaponics

Building your own DIY bell siphon is a cost-effective and rewarding way to ensure automatic water regulation in your aquaponics flood and drain system. A properly designed bell siphon eliminates the need for electrical timers while providing consistent water flow and oxygenation to plant roots.

Below we’ll walk you through the materials needed, step-by-step construction, and how to test and adjust your bell siphon for optimal performance.

Materials Needed for DIY Bell Siphon Construction

Before you begin, gather the following materials and tools:

Main Components of the Bell Siphon

1.PVC Pipes:

• Standpipe:Controls the maximum water level in the grow bed.
• Bell Dome:Creates the vacuum effect to start the siphon.
• Outer Guard (Gravel Guard):Protects the siphon from clogging due to grow media and debris.

2. Bulkhead Fitting:

Secures the siphon system to the grow bed base and provides a watertight seal.

3. Drill and Hole Saw:

For cutting holes in the pipes and grow bed.

4. Water-Resistant Sealant:

Prevents leaks around the bulkhead fitting and pipe connections.

Step-by-Step Guide to Bell Siphon Installation

Step 1: Prepare the Standpipe – Cut It to the Right Height

• Measure the desired water level in your grow bed.
• Cut the standpipe to this height using a PVC cutter or hacksaw.
• Attach the standpipe to the bulkhead fitting at the base of the grow bed.

Tip:The standpipe height determines the maximum water level before draining begins.

Step 2: Attach the Bell Dome – Ensure a Snug Fit

• Cut a larger PVC pipe that will act as the bell dome (about 1-2 inches taller than the standpipe).
• Drill small holes near the bottom of the bell dome to allow water to flow inside.
• Place the bell dome over the standpipe, ensuring it fits snugly but can still be removed for cleaning.

Tip: A taller bell dome helps create a strong vacuum effect for faster drainage.

Step 3: Install the Outer Guard – Prevents Debris from Clogging

• Use a larger PVC pipe or mesh tube as the outer guard.
• Drill multiple holes or slots along the guard to allow water flow while keeping out gravel and plant roots.
• Secure the guard around the bell dome, ensuring it stands upright in the grow bed.

Tip: The outer guard should be wide enough to allow easy removal of the bell dome for maintenance.

Step 4: Test the Siphon – Adjust for Optimal Water Flow Rate

1. Fill the grow bed with water and observe the water level rising.
2. Once the water reaches the standpipe height, check if the siphon triggers automatically.
3. Monitor how fast the water drains—if it drains too slowly, increase the hole size on the bell dome.
4. After draining, ensure the siphon breaks correctly, allowing the bed to refill.

Tip:If the siphon doesn’t break, try adding an air hole at the top of the bell dome.

How to Troubleshoot Bell Siphon Issues in Aquaponics Systems

Even with proper setup, bell siphons in aquaponics can sometimes experience operational issues that affect the flood and drain cycle. If your bell siphon is not starting, not breaking, or draining too slowly, these problems can disrupt water circulation, oxygenation, and nutrient delivery in your aquaponics system.

Below, we’ll go over common bell siphon problems, their causes, and practical solutions to ensure your system runs smoothly and efficiently.

Common Problems and Solutions

1. Bell Siphon Not Starting

If your bell siphon fails to trigger drainage, the issue is usually related to insufficient water flow or an incorrect standpipe height.

Possible Causes:

• The water is not reaching the siphon’s activation level.
• The pump flow rate is too slow.
• The standpipe is too high, preventing proper suction.

Solutions:

• Check water flow consistency: Ensure your pump is supplying enough water to fill the grow bed to the standpipe height.
• Adjust the standpipe height: If the standpipe is too tall, lower it slightly to ensure water overflows into it more easily.
• Increase pump flow rate:If water fills too slowly, the siphon may not activate properly. Try using a higher-flow pump.

Tip: A well-balanced siphon should trigger drainage as soon as the water reaches the standpipe top.

2. Siphon Not Breaking (Continuous Draining)

If the siphon doesn’t stop draining after the grow bed empties, it can prevent the bed from refilling properly, disrupting the flood-and-drain cycle.

Possible Causes:

• The air gap at the bottom of the bell dome is too small, preventing air from entering to break the vacuum.
• The outflow pipe angle is too steep, maintaining suction and prolonging drainage.

Solutions:

• Increase the air gap at the bottom of the bell dome: Cut larger holes or raise the bell dome slightly to allow air to enter faster.
• Adjust the outflow pipe angle:If the outlet pipe is angled too steeply, reduce the slope to slow water exit and help break the siphon.
• Drill a small air hole near the top of the bell dome: This allows air to enter and stop the siphon when draining is complete.

Tip:If your siphon won’t break, try lifting the bell dome slightly—if drainage stops, you need a larger air gap.

3. Slow Draining or Partial Siphoning

A slow or incomplete drain cycle can leave excess water in the grow bed, affecting plant oxygenation and causing root rot.

Possible Causes:

• Clogged grow media blocking the siphon intake.
• Standpipe diameter is too small, leading to weak suction.
• The bell dome holes are too small, restricting water flow.

Solutions:

• Clean grow media debris from the gravel guard:Check for clogs from roots, biofilm, or solid waste.
• Increase the standpipe diameter:A larger standpipe increases water flow and improves siphon activation.
• Drill larger holes in the bell dome:This allows water to enter the siphon faster, improving drainage speed.

Tip:If your siphon drains too slowly, try using a wider-diameter standpipe for better suction.

Recommended Bell Siphon Kits for Beginners

For those new to aquaponics or DIY systems, purchasing a pre-assembled bell siphon kit can simplify the setup process. These kits come with pre-cut components designed for efficient water flow and minimal adjustments.

Top-Rated Bell Siphon Kits for DIY Aquaponics

1️. AquaParts 12in Bell Siphon with Media Guard:Best for home systems with easy installation.
2️. Aquaponics CLEAR TOP Bell Siphon Kit: Best for IBC aquaponics sytems.

3️. HydroCycle Commercial Bell Siphon: Designed for large-scale aquaponics farms.

 

Frequently Asked Questions (FAQs) About Bell Siphons in Aquaponics

Bell siphons are an essential component of flood-and-drain aquaponics systems, but many beginners and even experienced users encounter questions about their setup, sizing, and optimization. Below, we answer some of the most frequently asked questions about bell siphons in aquaponics systems to help you troubleshoot issues and improve system efficiency.

1. How Do I Adjust the Water Flow Rate in a Bell Siphon?

 

The water flow rate in a bell siphon directly affects how efficiently it triggers and breaks. If the flow is too low, the siphon may never start, while too high a flow can cause incomplete drainage cycles.

Tips for Adjusting Water Flow in a Bell Siphon:

• Increase or decrease pump flow rate: A stronger pump will fill the grow bed faster, triggering the siphon sooner.
• Modify the standpipe height: A higher standpipe means more water needs to accumulate before draining starts. Lowering it triggers drainage sooner.
• Check outlet pipe positioning: Ensure the drainpipe angle isn’t too steep, as it can cause prolonged drainage cycles.

2. What Is the Best Size for a Bell Siphon in My Aquaponics System?

Choosing the correct bell siphon size ensures a proper flood-and-drain cycle based on your grow bed size and water volume.

Recommended Bell Siphon Sizes for Different Grow Bed Volumes

3. Why Is My Bell Siphon Not Starting?

If your siphon won’t trigger, check the water inflow rate and standpipe height.

Troubleshooting Steps:

• Ensure adequate water inflow: The bed must fill fast enough to trigger siphon activation.
• Check for air leaks: The bell dome should fit snugly over the standpipe.
• Adjust the standpipe height:A taller standpipe requires more water to trigger.

4. Why Won’t My Bell Siphon Stop Draining?

If the siphon won’t break, it might be due to poor air intake or an improperly positioned drainpipe.

Fixing a Stuck Siphon:

• Increase the air gap at the bottom of the bell dome.
• Adjust the outflow pipe angle:A steeper angle helps break suction.
• Use a breather tube:A small air tube inside the bell can speed up the break.

5. How Do I Prevent My Bell Siphon From Getting Clogged?

Clogs often occur when grow media, algae, or debris block the siphon components.

Preventative Measures:

• Use a gravel guard: This prevents media from blocking the standpipe.
• Regularly clean the siphon: Remove algae buildup and debris.
• Ensure proper media size:  Use expanded clay pebbles instead of fine gravel.

Conclusion

Bell siphons are a game-changer for media based aquaponics systems, offering a fully automated, energy-efficient, and low-maintenance solution for oxygenation and regulating water cycles. By choosing the right siphon size, adjusting water flow properly, and troubleshooting common issues, you can create an optimal growing environment that enhances plant health.

Now that you understand how bell siphons work and how to optimize them, why not take the next step?