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Undergravel Aquarium Filters

Are undergravel filters an outdated" piece of equipment for a freshwater aquarium?

By Jeremy Gosnell |

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Q. My local fish store (LFS) recommends using an undergravel filter in a freshwater aquarium. When I go to an online forum almost everyone tells me not to use one of these units. Should I use an undergravel filter like my LFS recommends or are they, as one forum user put it: “outdated.”
Sherry Turner

A. Undergravel filters were once a great piece of aquarium equipment that many fishkeepers used in their aquariums. In fact, it wasn’t that long ago that undegravel filters were standard in most any aquarium (marine or freshwater). I can remember some of my first freshwater aquariums that used undergravel filters with powerheads to promote good aquarium water quality. These plastic-bottomed units with two plastic tube risers are inexpensive and easy to use, likely one reason they became so popular. The undergravel filter argument is popular on Internet forums because there seems to be a core of aquarists that are still proponents of using them and many new aquarists that are totally against the idea.

Today, using an undergravel filter as your only means of filtration seems like a bad idea. With the technological advances in power filtration it seems out of place to solely rely on an undergravel filter. The theory behind undergravel filters is sound and simple. Undergravel filters employ your aquarium’s gravel as their filter media along with uneaten fish food and fish waste. They provide oxygen to the bacteria living within the gravel via a powerhead or airstone mounted at the top of the supplied plastic tubes. This encourages the bacterial breakdown of wastes.

While I can’t recommend using an undergravel filter as the only filtration for any aquarium, I will say that it is a tried and true method of bacterial filtration. It provides bacteria with the necessary elements it needs to proliferate and thrive. When used in conjunction with power filtration, an undergravel filter could be a decent aquarium keeping tool.

These units do require regular maintenance. One important thing to consider is gravel vacuuming. This process, done with a siphon, will remove excess waste particles from your gravel, freeing up room for oxygenation. This will prevent anaerobiosis, or the creation of areas in the gravel bed where bacteria are not efficiently working to break down wastes. You must be careful not to over vacuum your aquarium gravel and therefore remove so many microbes from the system that it enters biological shock. One recommendation is cleaning only 50 percent of your aquarium’s gravel per cleaning. Using this method you can rotate areas cleaned and not fear that you have removed too much beneficial bacteria from your aquarium.

One instance where an undergravel filter has no place is in either a reef aquarium or freshwater planted aquarium. In either instance the undergravel filter is a hindrance and does not combine well with the other items needed to make those aquariums flourish.

Undergravel filters appear to be little more than plastic plates and tubes and are not nearly as interesting as more modern forms of filtration. The truth is the undergravel filter is a proven piece of aquarium equipment that is inexpensive and easy to implement. Many traditional aquarists who keep freshwater aquariums still use undergravel filters with good success.

To help settle the debate you have experienced online, I’ll say this: Neither the LFS you visited nor the aquarium forum users you spoke with are right or wrong. The undergravel filter can be an effective piece of aquarium equipment. Anything that works efficiently, is inexpensive, and easy to use, is never really “outdated.”

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Reader Comments

Mike    Harrisburg, PA

1/23/2016 9:18:50 PM

I have maintained aquariums since about 1970. I learned early on that aquariums with an undergravel filter always remained clearer and the fish did better than those without. I will agree that newer filters of other types provide much better biological filtration than did earlier ones, perhaps making undergravel filters of less importance. In 1970, as today, you can maintain an aquarium without an udergravel filter. However, in my mind they provide the best option for biological filtration and I still use them (and my Discus are gorgeous). I do NOT recommend an undergravel filter as the only filter. A good mechanical filter should always be used. I use a canister filter and an undergravel filter and the results are superb. Yes, the gravel should be vacuumed from time to time, but I suspect most would do that anyway.

Terry    Myrtle Beach, SC

8/29/2015 5:46:00 PM

I am trying something different. I have a layer coral (salt water) substrate and a small layer of sand. Using 3 power heads pumping a little over 700 gallons an hour in a 55 gallon tank. I use to work at one of the major chains and a lot of the filters were basically designed just to keep you buying replacement materials. It will require some cleaning but trying to keep everything as natural as possible. It's a class project for my high school Marine Biology class.

Tony    FW, TX

2/2/2015 7:21:46 AM

I have used under gravel filters for many years since I started fish tanks as a hobby approximately 25 years ago. I have never had an issue with any tank using this type of filtration system!! I have always used powerheads and some type of whisper hanging or canister filter. I have seen comments stating that you can use the UGF without a hanging or canister bio filter but this is not true and not safe for the tank!! The purpose of the UGF is to remove uneaten food and waste that falls below the rocks. Without the UGF even if you used a syphon hose your still not going to clean everything under the rocks. The UGF provides a small space below the rocks for waste and uneaten food to fall. If you use a UGF without powerheads then there is really no point in using a UGF. The powerhead sucks out the waste from the bottom of the rocks and sends it back into the water to be filtered. As long as your using a good quality hanging filter or canister the waste will not contaminate the water because of the charcoal in the filter. This neutralizes the water and makes it safe! Also adding some water conditioner helps to remove the ammonia and other toxins in tap water that can hurt your fish. Overall I cannot say more good things about using a UGF. I have had many friends comment on how clean and crystal clear my water is and how I keep my fish growing and healthy! The bottom line is that UGF's might have been something of the past but they are still one of the best methods of filtration. Unfortunately the big companies that manufacturer quality UGF's (Perfecto,Lee's,Penn Plax) are no longer making them! Not sure which ones have discontinued them but they can still be found on ebay and amazon however the selection is narrowing fast as the last of the inventories are sold. Petco and Petsmart sell cheap UGF's that are pieced together so not sure how effective they are. Just make sure if you decide to use one that you also use a back hanging or canister filter and a powerhead or two. If you already have an underground filter don't listen to anyone telling you to remove it, you'll regret it! I just started three new tanks and I was able to find UGF's for all of them.

Emmit    Canton, OH

1/21/2015 11:31:42 AM

I've had aquariums since 1960, and most of them had under gravel filters and plants. It is absolutely not true that under gravel filters are not good for planted aquariums. The only trouble I've ever had with growing plants in gravel over a UG filter came when the plants outgrew the tank. The story about UGFs being bad came about when European growers invented a system that used sand and clay in the substrate. Naturally under gravel filters did not be work in such a system.
The trick to planting over an under gravel filter is to allow enough depth of gravel to accommodate the root systems of the plants. This can be done by banking the gravel, making it very deep at that back and series, and shallow in the front. Either air lifts or power heads seem to work. Air lifts are OK for tanks under 20 gallons, but powerheads are better for larger tanks. Every planted tank I have seen in my area used UG filters.

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