An undergravel filter (UGF) is a classic filtration system. It uses the natural substrate of your aquarium as part of the filtration process. It is inexpensive, easy to build, and a great choice for small to medium-sized aquariums, especially for beginners. In this guide, we’ll walk you through the steps to make a DIY undergravel filter. We will also show you how to improve it for your aquarium’s needs.
What is an Undergravel Filter?
An undergravel filter works by drawing water through the gravel bed, where beneficial bacteria break down harmful ammonia and nitrites. The filtered water is then recirculated back into the tank. This system combines mechanical filtration (removing debris) with biological filtration (promoting beneficial bacteria).
Benefits of an Undergravel Filter
- Cost-effective: Low setup and maintenance costs.
- Space-saving: No bulky equipment inside the tank.
- Encourages natural filtration: Uses the substrate as a medium for beneficial bacteria growth.
- Aeration: Ensures even oxygen flow throughout the tank.
Materials Needed
Before starting, gather the materials needed:
- PVC pipes (1/2″ or 3/4″ diameter)
- Air pump
- Airline tubing
- Air stone (optional)
- Gravel substrate (preferably medium-sized gravel)
Step-by-Step Instructions
Step 1: Measure and Cut the Base
- Measure the dimensions of your aquarium’s bottom.
- Ensure that the base covers the bottom fully, with minimal gaps along the edges.
Step 2: Prepare the PVC Pipe Framework
- Cut PVC pipes into sections:
- Long pieces for the length of the tank.
- Multiple short pieces for the width (depending on the tank size).
- Drill small holes or slots along the pipes to allow water to flow through.
- Assemble the pipes into a grid framework using PVC elbows or T-connectors.
Step 3: Attach the Uplift Tubes
- Add vertical PVC tubes (uplift tubes) to the back corners of the framework.
- The length of the tubes should extend from the base to just above the water surface.
- Secure the tubes with aquarium-safe silicone or zip ties.
Step 4: Add the Gravel Layer
- Place the assembled filter base in the tank.
- Ensure the gravel is evenly distributed for efficient filtration.
Step 5: Install the Pump System
For Air Pump Systems:
- Attach an air stone to the airline tubing (optional).
- Insert the air stone into the bottom of the uplift tubes.
- Connect the airline tubing to the air pump outside the tank.
- Turn on the pump to create airlift suction, drawing water through the gravel.
For Powerhead Systems:
- Attach a water pump or powerhead to the top of the uplift tubes.
- Position the pump to circulate water efficiently.
- Secure the pump with suction cups or brackets.
Step 6: Testing an Undergravel Filter
- Fill the aquarium with water.
- Turn on the air pump or powerhead and observe the water flow.
- Ensure water is being drawn through the gravel and exiting through the uplift tubes.
- Check for any leaks or uneven flow and make adjustments as needed.
Maintenance Tips
- Vacuum the Gravel Regularly: Over time, debris can accumulate in the substrate. Use a gravel vacuum during water changes to prevent clogging.
- Monitor Biological Load: Avoid overstocking the tank, as UGFs have limited capacity compared to advanced filtration systems.
- Clean the Uplift Tubes: Periodically check and clean the uplift tubes to maintain consistent water flow.
- Inspect Air Stones: Replace worn-out air stones to ensure optimal aeration and suction.
When to Use an Undergravel Filter
An undergravel filter is ideal for:
- Tanks with moderate bio-loads.
- Beginner aquariums with hardy fish.
- Small aquariums (10–40 gallons).
Note: Avoid UGFs in tanks with plants that need nutrient-rich substrates. Fine sand in tanks can also clog the device.
Creating a DIY undergravel filter is a rewarding project that can enhance your aquarium’s filtration system while saving money. By using these steps, you’ll have an efficient, eco-friendly solution tailored to your setup.