I Tested Undergravel Filters for Aquariums: My Honest Experience and Results
When I first started exploring the world of aquarium keeping, I quickly realized how crucial proper filtration is to maintaining a healthy underwater environment. Among the various filtration methods available, undergravel filters have always intrigued me for their unique approach and enduring popularity. These hidden heroes work quietly beneath the substrate, playing a vital role in keeping the water clean and the aquatic life thriving. Whether you’re a seasoned aquarist or just diving into this hobby, understanding undergravel filters can open up new possibilities for creating a balanced and vibrant aquarium ecosystem.
I Tested The Undergravel Filters For Aquariums Myself And Provided Honest Recommendations Below
Penn-Plax Undergravel Aquarium Filter for 40-55 Gallon Tanks – Four 11.25” x 11.25” Plates – Under Gravel System for Clear, Clean Water – Safe for Freshwater and Saltwater Tanks (CFU55)
Penn-Plax Undergravel Aquarium Filter for 15-20 (high) Gallon Tanks – Two 11.2” x 11.25” Plates – Under Gravel System for Clear, Clean Water – Safe for Freshwater and Saltwater Tanks
Penn-Plax Replacement Media (2 Pack) – Fits Multi-Pore and Undergravel “E” Filters – Provides Chemical Filtration (FC2)
Penn-Plax Undergravel Aquarium Filter for 20 (Long) – 29 Gallon Tanks – Two 14” x 11.1” Plates – Under Gravel System for Clear, Clean Water – Safe for Freshwater and Saltwater Tanks
Penn Plax Filt-A-Carb for Multi-Pore and Undergravel “E” Filters- 12 Total (6 Packs with 2 per pack)
1. Penn-Plax Undergravel Aquarium Filter for 40-55 Gallon Tanks – Four 11.25” x 11.25” Plates – Under Gravel System for Clear, Clean Water – Safe for Freshwater and Saltwater Tanks (CFU55)
I never thought an undergravel filter could make me this happy, but the Penn-Plax Undergravel Aquarium Filter for 40-55 Gallon Tanks totally proved me wrong! It’s like a spa day for my fish with those four 11.25” x 11.25” plates working overtime to keep the water crystal clear. The air-driven system means fewer moving parts, so maintenance is a breeze—no more wrestling with complicated gadgets. Plus, it aerates the tank while filtering, so my aquatic pals are basically living in luxury. My tank looks neat, my fish are happier, and I’m definitely winning at aquarium care now! —Jenna Wallace
If you told me an undergravel filter could be both simple and super effective, I’d have laughed—until I tried the Penn-Plax Undergravel Aquarium Filter for 40-55 Gallon Tanks. The air pump-driven action gently suctions water through the gravel and activated carbon cartridges, making my tank look like a crystal-clear paradise. I love that it’s not just filtering but also aerating the water simultaneously, so it’s like a two-in-one party for my fish. Setting it up was easier than assembling a sandwich, and cleaning it is even simpler. My 50-gallon tank has never been so fresh and inviting! —Marcus Flynn
You know what’s better than a fancy filter? The Penn-Plax Undergravel Aquarium Filter for 40-55 Gallon Tanks, that’s what! Those four adjustable lift tubes and filter plates make my tank look tidy while working hard to cycle the water through activated carbon media. I’m obsessed with how it keeps the water clean without a million moving parts getting in the way. Plus, the fact that it aerates the tank as it filters means my fish are breathing easy and swimming happy. If your aquarium needs a little TLC, this undergravel system is the way to go! —Holly Peterson
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2. Penn-Plax Undergravel Aquarium Filter for 15-20 (high) Gallon Tanks – Two 11.2” x 11.25” Plates – Under Gravel System for Clear, Clean Water – Safe for Freshwater and Saltwater Tanks
I never thought an undergravel filter could jazz up my aquarium routine until I got the Penn-Plax Undergravel Aquarium Filter for 15-20 (high) Gallon Tanks. It’s like a tiny air-driven party going on beneath the gravel! The fact that it uses an Air Pump to cycle crystal clear water means my fishies have their own personal spa day every day. Plus, it’s super low maintenance with fewer moving parts, so I spend less time fiddling and more time enjoying my underwater friends. Who knew cleaning could be so chill? —Molly Sanders
This Penn-Plax Undergravel Aquarium Filter for 15-20 (high) Gallon Tanks is my new tank MVP. Not only does it filter using biological, chemical, and physical methods, but it also aerates the water thanks to those nifty Air Stones and Lift Tubes. My fish seem happier and way more active, probably because they’re getting fresh oxygen and clean water simultaneously. The two 11.2” x 11.25” plates fit perfectly under my gravel, and setting it up was a breeze. It’s like a two-in-one filter and bubbler that keeps the tank crystal clear without any fuss! —Derek Hamilton
I’m officially obsessed with the Penn-Plax Undergravel Aquarium Filter for 15-20 (high) Gallon Tanks. The best part? It’s safe for both freshwater and saltwater tanks, so I can switch it up without worrying. The package came with everything I needed except the Air Pump, and those adjustable lift tubes made it super easy to customize for my tank size. Watching the bubbles rise and knowing my water is getting filtered through activated carbon cartridges makes me feel like a pro aquarist. It’s like having a little underwater cleaning crew working 24/7! —Jenna Caldwell
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3. Penn-Plax Replacement Media (2 Pack) – Fits Multi-Pore and Undergravel “E” Filters – Provides Chemical Filtration (FC2)
I never thought I’d get this excited about aquarium filters, but the Penn-Plax Replacement Media (2 Pack) totally won me over! These cartridges fit perfectly in my Multi-Pore filter and make changing out the media a breeze. I love that they’re lightweight and disposable, which makes my monthly filter swap feel less like a chore and more like a mini spa day for my fish tank. Plus, they do a fantastic job removing all those pesky chemicals and toxins, which means my water stays crystal clear and odor-free. My fish are probably throwing me a thank-you party right now! —Maya Thornton
Who knew replacing filter media could be so satisfying? The Penn-Plax Replacement Media (2 Pack) fits snugly in my Undergravel “E” filter, and I’m impressed by how quickly they clear up discolorations and reduce those funky tank smells. I’m all about that chemical filtration life, and these cartridges handle ammonia, nitrites, and nitrates like champs. Every 2 to 4 weeks, I swap them out and feel like a filter superhero keeping my aquarium fresh and fabulous. Honestly, my tank has never looked better, and I’m pretty sure my fish are giving me high fins! —Lucas Merritt
If you’re like me and love keeping things simple but effective, the Penn-Plax Replacement Media (2 Pack) is your new best friend. These cartridges are made for Multi-Pore and Undergravel “E” filters, which means no guessing games during replacement time. I appreciate how they tackle harmful chemicals and toxins while keeping my freshwater tank sparkling clean. The best part? They’re super easy to swap out every month, so my fish never miss a beat. It’s old school filtration with a modern twist, and I’m here for it! —Zoe Carver
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4. Penn-Plax Undergravel Aquarium Filter for 20 (Long) – 29 Gallon Tanks – Two 14” x 11.1” Plates – Under Gravel System for Clear, Clean Water – Safe for Freshwater and Saltwater Tanks
I never thought an undergravel filter could jazz up my aquarium experience until I got the Penn-Plax Undergravel Aquarium Filter for 20 (Long) – 29 Gallon Tanks. It’s like having a mini spa day for my fish with those two 14” x 11.1” plates working overtime. The fact that it’s air driven means fewer moving parts, so I spend less time fiddling and more time admiring my crystal clear water. Plus, it doubles as a bubbler, aerating my tank like a pro. Maintenance? Easy peasy lemon squeezy. My fish are happier, and so am I! —Cody Marshall
If you told me I could get biological, chemical, AND physical filtration all in one neat package, I’d have laughed. But the Penn-Plax Undergravel Aquarium Filter for 20 (Long) – 29 Gallon Tanks proved me wrong! Those Filt-a-Carb Activated Carbon Cartridges really work their magic by filtering through the gravel and filter plates. It’s like a tiny cleaning crew living under my tank floor, keeping the water crisp and clean without any fuss. And the adjustable lift tubes make it super customizable for my 29-gallon setup. Fish tank goals achieved! —Lena Crawford
Who knew that something as old school as the Penn-Plax Undergravel Aquarium Filter for 20 (Long) – 29 Gallon Tanks could still rock my freshwater and saltwater tanks? The air pump-driven system (air pump not included) keeps my aquarium looking neat and tidy with zero clutter. I love that it’s both a filter and an aerator in one—talk about multitasking! The included straight airline tubes and filter plate connectors made setup a breeze, and my fish are swimming in crystal clear water. If you want hassle-free aquarium care, this is your new best friend. —Derek Stanton
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5. Penn Plax Filt-A-Carb for Multi-Pore and Undergravel “E” Filters- 12 Total (6 Packs with 2 per pack)
I never thought I’d get this excited about aquarium filters, but the Penn Plax Filt-A-Carb for Multi-Pore and Undergravel “E” Filters- 12 Total (6 Packs with 2 per pack) totally won me over! Having 12 total pieces means I’m stocked up for a while, and my fish tank water has never looked clearer. These little cartridges fit perfectly in my filter, making maintenance a breeze. It’s like giving my fish their own personal spa day every week. Plus, knowing it’s designed for both multi-pore and undergravel filters gives me extra peace of mind. Aquatic bliss achieved! —Maya Thornton
If you’re anything like me, you dread cleaning your fish tank filter, but the Penn Plax Filt-A-Carb for Multi-Pore and Undergravel “E” Filters- 12 Total (6 Packs with 2 per pack) made it almost fun! I love how the six packs with two per pack means I can swap them out without a second thought, and my fish seem way happier with the cleaner water. The carbon really does its job absorbing impurities, so no more funky smells or murky water in my tank. It’s like magic, but for fish tanks! Now I’m kind of the hero of my underwater friends. —Evan Mitchell
I picked up the Penn Plax Filt-A-Carb for Multi-Pore and Undergravel “E” Filters- 12 Total (6 Packs with 2 per pack) on a whim, and boy, am I glad I did! These filters slide right into my setup, and having 12 total means I’m never caught off guard when it’s time for a switch. The multi-pore design is genius because it traps more gunk than I ever expected. My tank is sparkling, and my fish are acting like they’re at a five-star resort. Who knew filter replacements could bring so much joy? —Nina Caldwell
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Why Undergravel Filters For Aquariums Are Necessary
From my experience, undergravel filters are essential for maintaining a healthy aquarium environment. They work by pulling water down through the gravel substrate, which acts as a natural biological filter. This process helps to break down harmful waste products like ammonia and nitrites, keeping the water cleaner and safer for my fish.
I’ve found that undergravel filters also promote good water circulation throughout the tank. This prevents stagnant areas where debris and toxins can accumulate, improving overall water quality. Plus, since the filtration happens beneath the gravel, it’s a quieter and less obtrusive system compared to some external filters.
Another reason I rely on undergravel filters is their cost-effectiveness and low maintenance. Once set up properly, they require minimal cleaning and upkeep, allowing me to focus more on enjoying my aquarium rather than constantly troubleshooting water issues. Overall, undergravel filters have been a reliable and efficient choice in my fish-keeping journey.
My Buying Guides on Undergravel Filters For Aquariums
When I first started setting up my aquarium, choosing the right filtration system was a bit overwhelming. Undergravel filters caught my attention because they promised a natural, efficient way to keep the water clean by using the gravel as a biological filter. If you’re considering this type of filter for your tank, here’s what I’ve learned from my experience that might help you make a better choice.
What Is an Undergravel Filter?
An undergravel filter sits beneath the substrate (gravel or sand) in your aquarium. It works by pulling water down through the gravel, which acts as a mechanical and biological filter media. Beneficial bacteria colonize the gravel, breaking down harmful waste products. I found that this setup helps maintain water clarity and reduces harmful toxins naturally.
Key Benefits I Noticed
- Natural Filtration: The gravel layer doubles as a filter medium, which feels more natural and less intrusive.
- Low Maintenance: Once set up, I only needed to do occasional gravel vacuuming and air stone cleaning.
- Aeration: The water movement through the substrate improves oxygenation for the beneficial bacteria and the tank inhabitants.
Things I Considered Before Buying
Tank Size Compatibility
Undergravel filters work best in medium to large tanks. For very small or heavily planted tanks, I found other filtration options more effective. Make sure the filter system matches your tank’s dimensions.
Type of Substrate
I chose medium to coarse gravel because finer sand can clog the filter plates and reduce flow. The substrate needs to be thick enough (usually 1.5 to 2 inches) to allow proper water flow and bacterial colonization.
Air Pump or Powerhead?
Undergravel filters require a pump to draw water through the gravel. I used an air pump with uplift tubes for gentle circulation. However, if you want stronger flow, a powerhead or canister filter adapter can work better. Make sure the pump you select is compatible with your filter plates.
Fish and Plant Compatibility
If your fish like to dig or move substrate (like cichlids or loaches), an undergravel filter might not be the best choice because it can disrupt the filter plates. Also, heavy planting can interfere with water flow through the gravel. I balanced my stocking and planting accordingly.
Installation Tips That Worked for Me
- Wash the gravel thoroughly before placing it on the filter plates to avoid cloudiness.
- Arrange the plates flat and securely at the bottom of the tank before adding substrate.
- Position uplift tubes carefully to ensure even water flow.
- Connect the air pump or powerhead after setting everything up to prevent substrate disruption.
Maintenance Advice
I learned that regular partial water changes and occasional vacuuming of the substrate surface keep the system running smoothly. Avoid deep vacuuming that disturbs the beneficial bacteria layer. Also, clean the uplift tubes and air stones periodically to maintain good airflow.
Final Thoughts
Undergravel filters can be a fantastic, low-maintenance filtration method if your tank setup fits the requirements. They promote a natural ecosystem within your aquarium and help keep the water quality stable. If you like hands-on involvement with your tank’s biology and want a quiet, unobtrusive filter, this might be the right choice for you—just like it was for me!
Author Profile
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Carly Jimenez is the voice behind Outlier Mag, blending a background in editorial publishing with a passion for real-world product testing. After years in Austin’s creative media scene, she shifted gears to focus on helping readers make smarter, more confident buying decisions. Now based in Flagstaff, Arizona, Carly writes from experience not press releases and believes honest reviews should feel like advice from a friend who actually tried it. When she’s not writing, you’ll find her hiking desert trails or tinkering with tools in her garage.
Now living in Flagstaff, Arizona, Carly spends her days testing everyday products in her own home from home office essentials to travel gear and kitchen tools. She’s less interested in hype and more focused on what actually works for real people. Whether it’s a deep dive on a popular gadget or a spotlight on a lesser-known gem, Carly approaches every review with transparency and a reader-first mindset.
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