Undergravel Filter Aquarium: Complete Guide to Benefits, Setup, and Maintenance

Aquarium filtration is one of the most important aspects of fishkeeping. Without proper filtration, toxins like ammonia and nitrite can quickly build up, leading to stress, disease, or even death in aquarium fish. While modern aquariums often use canister filters, hang-on-back filters, or sponge filters, one of the oldest yet still relevant methods is the undergravel filter aquarium system.

The undergravel filter (UGF) has been used by aquarists for decades and remains popular due to its simplicity, affordability, and ability to biologically filter aquarium water. In this comprehensive guide, we’ll cover everything you need to know about undergravel filter aquariums, including how they work, their pros and cons, setup process, maintenance, and whether they’re suitable for your fish tank.

What is an Undergravel Filter Aquarium?

An undergravel filter aquarium uses a plastic plate placed beneath the aquarium substrate (usually gravel) with uplift tubes that allow water to circulate through the gravel bed. The gravel acts as both a mechanical and biological filter. As water flows through the substrate, beneficial bacteria colonize the gravel and break down harmful toxins into less harmful substances.

This system relies heavily on the nitrogen cycle, where ammonia from fish waste is converted into nitrite, and then into nitrate, which is less harmful in moderate concentrations. The undergravel filter provides a large surface area for bacterial growth, making it a natural biological filtration method.

How Does an Undergravel Filter Work?

1. Filter Plate Placement – A plastic filter plate is placed at the bottom of the aquarium.
2. Gravel Layer – Aquarium gravel (2–3 inches) is added on top of the plate.
3. Uplift Tubes – Tubes connected to the plate extend upwards, reaching the water’s surface.
4. Air Pump or Powerhead – An air pump with an air stone, or a powerhead, pushes water through the uplift tubes.
5. Water Flow – Water is drawn down through the gravel and up through the tubes, creating continuous circulation.

This process ensures water passes through the gravel, trapping debris and providing oxygen for beneficial bacteria to thrive.

Benefits of Using an Undergravel Filter Aquarium

Despite being considered “old school,” undergravel filters still offer several advantages:

1. Affordable Filtration Option

Undergravel filters are inexpensive compared to canister filters or sump systems. They are a cost-effective solution for beginners or those maintaining multiple tanks.

2. Biological Filtration

UGFs are excellent at supporting colonies of beneficial bacteria. The gravel bed provides a huge surface area for nitrifying bacteria to grow, helping keep ammonia and nitrite under control.

3. Low Maintenance

Unlike sponge or canister filters, which need frequent cleaning, an undergravel filter requires minimal maintenance. Regular gravel vacuuming is usually enough to keep the system efficient.

4. No Visible Equipment

Because the filter plate is hidden under the substrate, the aquarium maintains a clean and natural look. Only uplift tubes are visible, which can be positioned at the back to reduce visual impact.

5. Oxygenation of Substrate

The constant water flow through the gravel bed prevents anaerobic zones (oxygen-deprived areas that produce harmful gases). This makes it safer for fish and plants.

Drawbacks of an Undergravel Filter Aquarium

Like any filtration system, undergravel filters have some disadvantages:

1. Limited Mechanical Filtration

UGFs are not very effective at removing fine particles from the water. They mainly trap debris in the gravel, which requires manual cleaning.

2. Restricted to Gravel Substrates

They only work with gravel. Sand or very fine substrates clog the filter and restrict water flow.

3. Not Ideal for Heavily Stocked Tanks

Heavily stocked aquariums or tanks with large, messy fish (like goldfish or cichlids) may overwhelm the system, leading to poor water quality.

4. Plant Growth Limitations

Rooted plants may struggle in an undergravel filter system since water circulation can disturb their root zones.

5. Maintenance Can Be Tricky

If debris builds up under the filter plate, it can be hard to clean without dismantling the tank.

Setting Up an Undergravel Filter Aquarium

If you want to try a UGF, here’s a step-by-step setup guide:

Step 1: Choose the Right Tank and Filter Plate

• Select an undergravel filter that fits the size of your aquarium.
• Most UGFs are modular, so you can combine plates for larger tanks.

Step 2: Install the Filter Plate

• Place the plate on the bottom of the tank.
• Make sure uplift tubes are firmly connected.

Step 3: Add Gravel

• Use gravel with medium-sized grains (2–5 mm).
• Add 2–3 inches of gravel above the filter plate.

Step 4: Attach Air Pump or Powerhead

• Connect an air pump with an air stone to the uplift tube, or attach a powerhead for stronger water flow.

Step 5: Fill the Tank and Cycle It

• Slowly add water to avoid disturbing the gravel.
• Start the nitrogen cycle by adding fish food, ammonia, or hardy fish.

Step 6: Stock the Aquarium

• Once the cycle is complete (usually 4–6 weeks), introduce fish gradually.

Best Practices for Undergravel Filter Maintenance

To keep your undergravel filter aquarium running smoothly:

1. Gravel Vacuuming – Use an aquarium siphon weekly to remove debris trapped in the gravel.
2. Partial Water Changes – Perform 20–30% water changes weekly to control nitrates.
3. Check Air Pump/Powerhead – Ensure proper water flow through the uplift tubes.
4. Monitor Water Parameters – Regularly test ammonia, nitrite, nitrate, and pH.
5. Avoid Overfeeding – Excess food leads to faster clogging of gravel.

Fish and Aquariums Best Suited for Undergravel Filters

Undergravel filters work best in:

• Small to medium aquariums (10–55 gallons).
• Lightly stocked community tanks.
• Hardy fish species like guppies, tetras, mollies, and danios.
• Beginner aquariums where budget-friendly filtration is preferred.

They are less suitable for:

• Goldfish tanks (produce too much waste).
• Cichlid tanks (digging disturbs substrate).
• Planted tanks with rooted plants.

Comparing Undergravel Filters with Other Aquarium Filters

Conclusion

The undergravel filter aquarium remains a reliable and affordable filtration option for many aquarists. While it may not match the power and versatility of modern canister or sump systems, it excels in simplicity and biological filtration. If you maintain a lightly stocked aquarium with hardy fish, a UGF can provide crystal-clear, healthy water with minimal upkeep.

Whether you’re a beginner or an experienced aquarist who enjoys “old school” methods, undergravel filters still have a place in the fishkeeping world.

FAQs About Undergravel Filter Aquariums

Q1. Is an undergravel filter good for beginners?
Yes, UGFs are beginner-friendly because they are inexpensive, easy to install, and low maintenance.

Q2. Can I use sand with an undergravel filter?
No, sand will clog the filter. Only medium-sized gravel works properly.

Q3. How often should I clean an undergravel filter?
Weekly gravel vacuuming and regular water changes are enough. You don’t need to dismantle the filter unless it’s clogged.

Q4. Are undergravel filters good for goldfish?
Not recommended. Goldfish produce a lot of waste that can overwhelm the filter.

Q5. Can I use live plants with an undergravel filter?
Some plants with minimal root systems may work, but rooted plants usually struggle due to substrate disturbance.

Q6. What size tank is best for an undergravel filter?
UGFs work best in aquariums between 10–55 gallons that are lightly stocked.

Q7. Can I combine an undergravel filter with other filters?
Yes, many aquarists use UGFs alongside sponge filters or hang-on-back filters for added mechanical and chemical filtration.