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Just picked up a used 55gal that was run w/ an under gravel power headed filter and a canister..
I was thinking about using this as a dirted tank and am considering re-installing the under gravel filter..
This is really a 2 topic question though.
One is there a plant advantage to an under gravel filter? i.e getting more oxygen to the roots.
Two is it worth even bothering w/ using it?
Three if it has a benefit how does one lay out the substrate. Seems there would be a need for gravel/dirt/gravel(sand) so as to prolong its effective life.
Last what IS its usable lifespan b4 clogging? Never used under gravel b4. The orig tank used just colored aq. gravel and I do have that still but w/ dirted(sand) I can see finer particles eventually getting under the plates..

I understand the limits of this type of thing for filtering, and probably will run the canister as well and I'm not sure I want all the extra "stuff" in this tank (tubes/powerheads) unless there is a good reason. Thanks..
 

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UGF works like this:
Water is pulled out from under the plates with the pump.
Water flows through the gravel, bringing oxygen and ammonia through the gravel. This rich supply of oxygen and ammonia encouraged a very large growth of nitrifying bacteria on the surface of all the gravel. It becomes a very good bio filter.

This system breaks down when the particles of the substrate are too fine for water to move easily though the substrate.

A planted tank does not need this much surface area for bacteria. The plants are part of the bio filter, and plenty of bacteria will grow in the canister if it is handled right.

There is no good reason for keeping a UGF in a planted tank, and several reasons not to.

When I had them, and just started introducing plants, the plants did not grow very well.
Some of my tanks were an odd size or shape and the UGF plates did not fill the bottom area. Where the plants grew away from the plated they did a lot better.
 

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What about getting more oxygen to the roots. Is it simialar to hydroponics where added o2 to roots in submersed setting will add more benefit to the plants. Currently there is little water flow in the substrate and i suspect little oxygen.

I was kind of thinking along the lines of a reversed normal under ground filter instead of powerhead pulling water down into the substrate what about output pushing freash o2/co2 water up through the substrate. Of course using larger heavelier substrate would be required to prevent dislodging the substrate into the water column and mking it cloudy water?
 

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I wouldn't even consider a UGF with a dirt substrate. I found that a RFUG worked pretty good when I used it with pool filter sand, but the very fine particles with a dirt substrate would cause a mess if used with the UGF or RFUG. This is just an intuitive comment, because I didn't try it when I used a dirt substrate, but I'm pretty sure it would be a problem. The benefits from using that type filter are slight, if any, so it's just not worth taking that risk.
 

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I think the dirt would fall through the slots and be pushed out back into the water column creating a muddy mess. I could see the same happening in a reverse flow setup but not to the same extreme. Roots will grow down into the filter slots decreasing efficiency and making plant removal much more difficult. As has been mentioned no reason to use one and lots of reasons it is a really bad idea.
 
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