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What are the pros and cons of an undergravel filter?

This is a discussion on What are the pros and cons of an undergravel filter? within the FreshWater General Discussion forums, part of the FreshWater Topics category;
No matter how often I do water changes, I always seem to have a ton of junk come up with ...

  1. #1
    Little Fish Praetorian27's Avatar
    Join Date
    Jun 2007
    Albany NY area

    Default What are the pros and cons of an undergravel filter?

    No matter how often I do water changes, I always seem to have a ton of junk come up with my Python through the gravel. Also, I am having big Nitrate problems. I have a 30 gallon community tank and can't seem to get my nitrates down any lower than 10 ppm! I checked the water straight from the tap...0 ppm. I did a 50 % water change today and the nitrate was still high. I have lost 4 fish this past two weeks and think it must be the nitrates since I checked all over levels and they were fine. I did about 80-85 % water change and the nitrates are still 10 ppm. I know 10 isn't super high...but is it a good level for the tank? The fish that died looked fine, until they stopped swimming and were dead the next morning. They didn't all die the same night, just over the course of two weeks. There were no signs of disease on any of them.

    I have heard that undergravel filters help fight nitrates because it is constantly filtering the gravel. But I have also heard that there are problems with them. What do you guys think?

    30 Gallon Community Tank:

    5 XL Neon Tetras
    4 Pineapple Swordtail
    5 Ghost Glass Cats
    2 Red Tailed Columbian Tetras
    1 Flying Fox
    1 Gourami
    1 Small Pleco
    LOTS of plants!

    55 Gallon - Awaiting setup

  2. #2
    Medium Fish cchase85's Avatar
    Join Date
    Jun 2006
    New England


    They are next to impossible to clean, are difficult in a planted tank, end up being a source of pollutant unless regularly cleaned, and offer no "real" place for beneficial bacteria to grow.

    I am sure someone else can list some pros.

    EDIT: And 10ppm is fine for fish, even fish that are sensitive to nitrates should be fine at 10ppm.
    Last edited by cchase85; 10-28-2007 at 07:53 PM.
    29g planted - rainbows, tetras, corys, plecos
    10g - being set up in 2 weeks
    5.5g planted - pygmy corys, pristella tetras
    2g planted - cherry shrimp

  3. #3
    Super Fish CAPSLOCK's Avatar
    Join Date
    Jul 2004
    Cape Cod


    I think some people have success with them if they set them up with reverse flow.

    Other than that, it's pretty much old technology that ends up being more trouble than it's worth. You have to take out all the gravel when you want to clean them, and they collect a lot of gunk underneath.

    You might consider adding some low light plants (assuming you're using the hood/light that came with the tank) to help lower the nitrates. Java fern is a good one... it's basically impossible to kill.
    40g Breeder SW - softie reef started 5/2/13! Percula clown, neon blue goby, tailspot blenny, royal gramma, pearly jawfish, flame angel, possum wrasse, firefish
    20g Long Planted - started 7/2/14! Celestial pearl danios, sparkling gouramis, dwarf habrosus cories

  4. #4
    Super Fish big54bob's Avatar
    Join Date
    Dec 2006
    On my office chair playing Runescape


    Crabs+UGF equals a big pain.
    My fidler crab tried crawling under the ugf in my 29gal. Thank god i ripped it out.

  5. #5
    Super Fish MissFishy's Avatar
    Join Date
    Aug 2006


    Undergravel filters are old filtering technology. They really do nothing but trap gunk under them, which can of course lead to nitrate levels rising. With so many newer technologies out there, there is no reason to have these anymore. Ditch it and get a HOB.

    The only way to have an undergravel filter be beneficial is to set up a reverse flow UGF. This can be difficult to do correctly. Just the fact that everytime you gravel vac tons of gunk comes up is telling me you need to just get rid of it and get a good HOB to filter out the water.
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  6. #6
    Little Fish HMarcks's Avatar
    Join Date
    Aug 2007
    Palm Springs


    Could the tons of junk be due to over feeding and rotting plants? And as long as the nitrites and amonnia are at zero isn't a constant 10ppm of nitrates a good thing? Thats what I have been assuming with my tanks.
    135gal fresh water planted community
    29gal Lake Tanganyika, Neolamprologus multifasciatus & synodontis petricola
    12gal salt pair of small clown fish and corals

  7. #7
    Moderator Lotus's Avatar
    Join Date
    Aug 2003
    Southern California


    While nitrates under 20ppm is generally considered healthy for most fish, of course the lower the better.

    I think your main problem is that your tank is overstocked. Once you have your 55g up and running, you should rethink your stocking plans.

    I'd say an undergravel filter isn't your answer. As others said, they're less efficient than HOB or canister filters.
    Lotus and Ecotank's tanks

    "So long, and thanks for all the fish."

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