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Using Undergravel Filters to Their Full Potential

Undergravel FilterWith all of the technological advances in the aquarium hobby, I thought it would be nice to take a look at one of the most rudimentary and long-standing pieces of equipment in the industry – the Undergravel Filter.

Undergravel filters get a pretty bad rap. They are sometimes considered to be a relic of aquarium history, but are they still serviceable? Some hobbyists swear by them and some hobbyists swear at them. How your tank runs using an undergravel filter is dependent on a couple of factors – set up and maintenance. Let’s take a look at some of the common problems associated with undergravel filters and explore some solutions.

The Problem: They don’t work well enough. Some say undergravel filters are inefficient in tanks that have a lot of fish.

The Fix: Proper set-up is very important with filtration. This is especially true of undergravel filtration. Using the proper size and amount of gravel plays an important role in how well your filter will function. To ensure maximum efficiency with your filter, you will need to make sure that you have at least 2 to 3 inches of gravel above the filter plate. The gravel should be of mixed grades, but make sure that you don’t have anything so small that can slip under or through the grating. You will also want the gravel to be evenly distributed across the bottom. Since water flow follows the path of least resistance, an area with less gravel will receive more flow than areas that have more gravel. This will result in less efficient use of the entire filter plate. Another thing to look out for is the use of large pieces of stone or wood that sit flat on the gravel. These ornaments can restrict flow over the area. 

Another recommendation: Use compressed sand airstones instead of the compressed paper ones. Paper airstones get clogged up quickly. You should change airstones out every month regardless of which ones you use, but the sand airstones will work better for longer periods of time.

The Problem: They are DIRTY! Many hobbyists have horror stories about the amount of gunk that builds up beneath the filters over the course of years. Another complaint is that they’re a pain to maintain.

The Fix: Fish waste and other detritus is pulled down through an deposited under the filter plate, so it is easy to understand why someone might consider them to be dirty. People assume that you should not siphon the gravel if you have undergravel filtration, thinking it will destroy or suck up the beneficial bacteria. However, proper maintenance will ensure that excessive waste and detritus do not build up underneath the plate.

planted displayTo keep your filtration running at peak performance you should perform weekly water changes. Mentally divide your tank into quarters. Each week, select a quarter of the tank and siphon the gravel in that section. Using your gravel siphon, go about a half inch down into the gravel. This should remove a good amount of the gunk that settles under the filter plate while keeping the bacterial colonies from being totally wiped out. It should also allow the bacteria to repopulate the area before you have to siphon the next section. By following this regimen, your undergravel filter should not accumulate excessive waste or produce nitrates in large amounts.

Simply put, undergravel filtration has been around so long because they do work. The low-tech and simple piece of equipment can be used successfully for years when maintained properly. Keep your tank stocked properly (don’t overload), don’t over feed, and do water changes on schedule. You should have the same success with an undergravel filter as you would with more advanced filtration techniques on the market today.  Give an undergravel filter a chance…with proper set-up and maintenance in can be a reliable and cost-effective tool.



  1. avatar

    Hi Craig,
    Thanks for addressing this – wonderful article; I’m been meaning to cover UG filters on thatreptileblog, they are indispensable for tadpoles and small salamanders, very useful for many others also.

    My grandfather and I were introduced to UG filters via Robert Straugham’s classic, The Salt Water Aquarium in the Home. At the time (early-mid 60’s), they were salt water gold-standards and we had great luck with exotic and native fishes, as well as messy feeders such as blue claw crabs.

    I’ve used UG as sole filtration for large tanks housing sunfishes, bass, bullheads, and in zoos for exhibits with animals that produce a good deal of ammonia, including tentacled snakes and water snakes. Water quality was excellent, as evidenced by tests and the fact that food fishes lived and fed in the tanks (tentacled snakes) until captured.

    One aquarium with native fishes went over 20 years without being broken down…it was well planted also, and nearly impossible to foul..even via deaths of large fishes.

    One commercial aquarium that I work with today` uses UG filters as sole filtration on huge exhibits housing pollack, dog fish and other large fishes.

    I agree that the key lies in those points you’ve mentioned – water changes, gravel cleaning. if set up and serviced as you describe, a UG is hard to beat.

    I’ve had some luck in removing extra detritus from below plate by attaching a siphon to hole in which the upright discharge tube rests, but fit needs to be secure. I once kept a large exhibit with mudskippers and archer fishes in great condition for many years using a reverse-flow UG with power heads – this cut down on gunk below the plate.

    Thanks again, Frank

  2. avatar

    I maintained a 55 gallon freshwater setup with two breeding pair of angelfish for 12 years without ever having to break down the system for cleaning. I operated an undergravel filter across the full length of the tank, two high flow power heads, one on each end. Under the filter plate I placed a 1/2 Inch thick piece of polyester batting (bought at the local fabric shop), this was to increase the area available for the proper growth of bacteria. On top of the filter plate was three inches of fine gravel, with two inches of medium gravel on top of that, and another inch of polished river stone on that. There was a secondary hang on back filter with carbon media for extra clarity in the water. Once every two weeks I would vacuum the surface of the river stone, gently enough that the stones were never displaced, and water was only changed out 1/4 per month, and topped offwhen needed because of evaporation. I think, when properly set up the under gravel filter is the best way to go. Had I not moved to a new home ten years ago I would probably still have this same setup.

  3. avatar

    do you recommend a particular undergravel fllter?

  4. avatar

    Hello Jennifer, Undergravel filters have been decreasing in popularity and we actually only sell one brand of them at this point, the Lee’s Economy Undergravel Filter. For the most part, all undergravel filters function the same in my opinion and I couldn’t recommend one over another in terms of effectiveness. Our Choosing An Aquarium Filter blog may be helpful to you to help choose one that works best for you.

  5. avatar

    Are there any considerations when using an undergravel filter with live plants?

  6. avatar

    Hi Lou, Undergravel filters usually don’t work with live plants because the roots of the plants can clog up the area under the filter or restrict flow through the substrate.

  7. avatar

    On certain size tanks, one can purchase an under-gravel filter that comprises of one whole plate, which covers the bottom, or two plates. Is either type, better than the other? and why?

  8. avatar

    Hello Ken, Both would function the same. It is simply a matter of manufacturer specifications and personal preference.

  9. avatar

    I will get another under-gravel filter but I can’t remember how I got the air to both corners of the under -gravel filter. SO what kind of pump do I need? TY!

  10. avatar

    Hello Terri, It depends on the type of filter. Some use pumps while others use airstones. You would want to check with the specificiations on the filter you choose.

  11. avatar

    Eileen Daub, It package doesn’t say. It’s just an underground filter. I ‘figure’ airstones will not do how underground filters are supposed to work. So are you saying I can use airstones OR powerheads ? I just don’ t understand. THANK YOU! 🙂
    (My initial email question and your response is copied/pasted below).

    I will get another under-gravel filter but I can’t remember how I got the air to both corners of the under -gravel filter. SO what kind of pump do I need? TY!

    Eileen Daub June 1, 2017 at 8:20 am

    Hello Terri, It depends on the type of filter. Some use pumps while others use airstones. You would want to check with the specificiations on the filter you choose.

  12. avatar

    Hello Terri, Different types of undergravel filters will use different equipment to make them work. All undergravel filters will usually have two rigid tubes connected to the plates. One specific undergravel filter will use air stones within the tube while a different model will use a pump connected to the top of the tubes. For example, this undergravel filter by Lee’s uses airstones within the tubes while others may have a powerhead attached to the tops of the tubes. If you can tell me the brand and model of the one you have, I might be able to give you more information about it specifically.

  13. avatar

    Terri, how big is the tank you’ll be putting the filter in? I always throw away the air stone caps that come with the undergravel filters and replace them with power heads, most of the power heads have a graduated fitting so they will fit almost any tube. On one of my setups I have adjustable flow heads so I can choose how much they push the water, on another I just have high flow.

  14. avatar

    Some undergravel filters are made to be adaptable to either airstones or powerheads for a bit more power. Not all can be used that way but it is an option for a lot of the brands on the market now.

  15. avatar

    ROBERT, It is a 20 gallon. Maybe 25. 40 years ago it DOES seem like I had what you mentioned ‘graduated fitting’ – so it must have been power heads. My fish were SO happy back then and I am wanting to do the same setup (under-gravel filter). I ‘think’ I remember have two power heads and it was the same size tank as the one I want to set up now. I have not bought an under-gravel filter yet (because want to get that and the power head – apparently is what I want – per your note WHICH I appreciate SO MUCH). Anyother info would be so nice. Thank you Robert,
    Also, I’d like to have plants but what I’ve read said don’t plant on bottom of under-gravel filters. Do you? Terri

  16. avatar

    Hello Terri, Undergravel filters are generally not suitable for tanks with live plants. The roots of the plants will usually clog the undergravel filter and prevent it from working correctly. I wouldn’t recommend using an undergravel filter if you plan on having live plants in the tank; a more advanced filter like a canister filter would be much better for you for that type of tank.

  17. avatar

    Terri, one of my current setups with undergravel filter is planted but the plants are not in the gravel at the bottom of the aquarium. I have the back three to four inches of the tank terraced with red lava rock from a local quarry that i drilled some small holes to run fishing line to anchor java moss, which can be a nightmare if you neglect it at all. I would not plant anything directly in the substrate.

  18. avatar

    Robert, you have been SO HELPFUL – thank you so much! TERRI

  19. avatar

    Always nice when hobbyists can share experiences and help each other out!

  20. avatar

    I just got an undergravel filter. I keep reading that the top part with the carbon in it is not good, should I take it off ? And I also have an air stone in there and think that my air pump is not strong enough to do both, because water doesn’t always come all the way out the top and cycle thru, so I need a recommendation for either a stronger air pump that can do both the filter and an air stone or just a air pump for the undergravel filter please and thanks much. I’ve been having such a hard time trying to research until I found your site.

  21. avatar

    Hello Mallarey, Using carbon with an undergravel filter is fine as long as it doesn’t affect the flow; just be sure to change the carbon at least monthly, depending on the bioload of the tank. I wouldn’t be able to recommend a proper pump or airstone without more info about the size of the tank, size of the undergravel filter, height of lift, etc.. If you need assistance in choosing the proper equipment, feel free to give our Fish Supplies staff a call at 717-299-5691 (option 3).

  22. avatar

    I use an Undergravel filter as well for my 55 gallon tank and personally love them i have always used them since my dad used them while i was young and he highly recommended that i use one also when i set up my first tank 20 years ago now !

  23. avatar

    Hi there, I’d like to say that UGF’s are ideal in a tank with live plants.
    Indeed, the roots do grow into the filter plates, but this supplies the plants with nutrition like nothing else!
    I run heavily planted, highly-stocked aquariums on nothing but UGF’s and everything thrives!

  24. avatar

    Hi Michael, I’m glad you have success with them. In most cases, the roots will eventually clog the area under the filter plate and it will no longer function as an undergravel filter.

  25. avatar

    I want to add an undergravel filter to my tank but I need some help deciding on the type. Many years ago, my first fish tank had a zig-zag style UGF. But the flat ones seem to be more common right now.
    Do you have recommendations of one type over the other?

  26. avatar

    Hi Kathryn, Either style is equally effective.

  27. avatar
    Jessica Leigh Rose

    Hello, can I use an under gravel filter without gravel for my axolotl tank? If not could I just lay filter floss over it like a carpet instead of using gravel?

  28. avatar

    Hi Jessica, An undergravel filter should work the same way with filter floss over it instead of gravel, as long as the water can pass through it the same way.

  29. avatar

    I’m setting up a new tank today, and have the UG filter set up with a powerhead resting (it doesn’t fit snugly inside the tubing, I’m assuming that’s how it’s supposed to be?) on right hand side resting on tube inserted into the UG plate. Should I also put a tube in the left side, and do I connect that to a separate air pump? Thank you!

  30. avatar

    Hi Linda, The exact configuration of the undergravel filter and the pumps or powerheads depends on the model you choose and without knowing what type you have, it would be difficult for me to say. I would recommend contacting the manufacturer of the one you have for questions about it. Generally speaking, an undergravel filter would use airstones OR powerheads, not both. Powerheads should fit snugly at the top of the pipe so the suction that drives the undergravel filter works correctly. If you are using airstones and not powerheads, you could use the same pump as long as it is powerful enough for both airstones.

  31. avatar

    Hi. Thanks for this blog. I’ve been wanting to put a UG filter for my 65G discus tank. Got a few questions thou:
    1. How thick of gravel should I put on top of the UG filter?
    2. How often do you have to gravel vac and how deep?
    3. Do you ever need to vac underneath? If yes, I guess that means dismantling the whole thing?


  32. avatar

    Hello Xavier, If you are planning on doing live plants in the tank, I wouldn’t recommend using an undergravel as the roots will clog the area under the filter and make it ineffective and potentially dangerous. As mentioned in this blog, the gravel should be about 2-3 inches deep on top of the plate and you should do regular siphoning and maintenance as described here. You should never need to completely dismantle the filter if you follow the procedures in this blog.

  33. avatar

    Hi Eileen,
    I am thinking of using an UGF but I plan to redirect the flow up gently through the gravel and with airstone under the filter. Any thoughts?

  34. avatar

    Hi Michael, The filter wouldn’t work if the flow is going up through it.

  35. avatar

    I’m about to set up a new 29 gallon fresh water aquarium. I had several aquarium set ups some years back that were based on suggestions a brochure from the Ginger Products Company to encourage a minimum amount of maintenance. They suggested using both and under gravel filter AND a power filter. In setting up the under gravel filter, they recommended using a section of “bio-substrate under gravel filter overlay.” Essentially the cottony material used in other types of filtration. They said this would increase the biological action of the under gravel filter making it more efficient. The brochure maintained that, without the “under gravel filter overlay” you can forget about 20-minute maintenance every two weeks and healthier fish. so, in the past I set up my aquariums this way and it worked very well. My question: Now it’s 2020. The Ginger Company is out of business (I think) So where can I find the kind of filter overlay material I used years ago. Is it just typical filter material or something more?

  36. avatar

    Hi Eric, That isn’t a brand that we have ever carried so I’m not familiar with the model you are referring to. I wouldn’t recommend adding filter media under an undergravel filter plate since that would affect the flow and effectiveness of the filter but if it is something you would like to do, any biological media should work. It is simply a surface for bacteria to grow on so any biological media with a high surface area would work the same. Floss and filter pads aren’t usually used as biological filtration since they can become clogged but you can view our selection of biological media on our website to find something that will work for you. Undergravel filters in general are not nearly as effective as other filtration methods – especially since most modern filters have biological filtration built into them – and are nearly obsolete at this point.

  37. avatar

    Hello. I am just new hobbyist. Recently, I learned about under gravel filter and bought new one. After testing it with my 20 gallons tank I wanted to use it for my 60 gallons tank. But the problem is my UGF is small and it covers only a fraction of my big tank. Will it work properly? Or should I buy big UFG so that whole tank floor is covered? Thank you.

  38. avatar

    Hi bataa, An undersized udergravel filter wouldn’t be of much benefit. All filtration should be properly-sized for the size of the tank. Undergravel filters especially are less effective than other types of filtration and one that isn’t the right size wouldn’t be of much help to the tank.

  39. avatar

    Been using UGF since 1976. Never ever had a problem.
    Used many other types of filters too.they all seem to work fine as well
    But I went full circle. Going back to the old school style simply because UGF Is cheaper..plus I missed that wonderful sound of the babbling brook effect. I just love a good babbling brook.

  40. avatar

    I installed a UGF in my tank when I started a new 29 gallon tank. Then 4ish months later the water turned green. After trying everything I could think of for 3ish months I gave in and tore down the tank and found a lot of buildup under my UGF. I had been doing bi weekly gravel cleaning with a siphon. Now I’m trying to determine if I should try the UGF again or not and if so do I need to do anything different. I liked that the water seemed cleaner than the tank I had without a UGF but I can’t tear down the tank every 7 months.
    When cleaning should I just siphon the gravel or put the siphon down the tube?
    Any other advice to avoid the green water again?

  41. avatar

    Hi Jennifer, All of that trapped waste is unfortunately how an undergravel filter works and one of the drawbacks of it. The green water usually comes from high Phosphate levels which may come from trapped waste and leftover food but can also come in with your water source. If you are using tap water or well water, be sure to test that as well as your tank to see if it has high Phosphate levels already. If it does, you may want to consider switching your water source or using a Phosphate-removing filter media. Be sure to keep up with regular water changes as well once your tank has finishing cycling again and limit the light on the tank to no more than 8-10 hours. Our blog articles Why Is My Aquarium Water Cloudy? and Phosphates – Invisible Troublemakers in Ponds and Aquariums may help you understand what is happening here as well.

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