# "Reverse Flow" Undergravel Filter Explanation Please?



## Danimals (Sep 15, 2011)

I was reading about undergravel filters and researching new ideas on how to filter my future breeder tank and came across and interesting concept, the reverse flow UGF. From what I'm gathering it's the same as a regular UGF except the outflow/inflow are reversed and water gets pushed out thru the gravel? 

I'm having a little bit of trouble grasping this concept, wouldn't that send substrate flying everywhere, among other things? 

If someone can help clear things up for me that'd be greatly appreciated! =)


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## oldpunk78 (Nov 1, 2008)

I believe Hoppy wrote a how to in the DIY forum. I'd do a search there.


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## wetworks (Jul 22, 2011)

What you need to do this properly is a power-head that allows you to reverse the flow. Because the outflow is spread out over the entire surface area of the undergravel plate, it does not make a mess at all. I used to use these as my only filter in my breeding tanks, and regardless of which direction you go (regular or reverse flow) you should switch for a bit every few weeks to keep from building up big colonies of anaerobic bacteria.


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## DaveK (Jul 10, 2010)

In my opinion, there isn't much difference between normal flow and reverse flow under gravel filters. It's more a question of what direction are your going to trap the dirt from. Quite a few years ago, reverse flow under gravel filters were "all the rage". Like many other things, the aquarium hobby goes through fads. 

I've actually use under gravel filters in FW and SW in both normal and reverse flow configurations. No matter what you do, you will get all the inherent issues. The biggest one is that it is impossible to get an even flow through one. This goes double if you are keeping fish that love to dig. The other big factor is that that are major dirt traps, something you usually do not want. 

When you mention breeder tank, I'm not sure if your talking about a small tank used to actually breed fish, or a tank like a 40 gal breeder used as a display tank. 

If it's a tank to actually breed fish, I'd use sponge filters rather than under gravel. If this is a display tank, my preference would be a canister filter that is large enough to contain the bio-media in it, or a hang on tank filter that has bio-media in one form or another. 

Since you now have the bio-media in the filter system, there is no need to use under gravel filters. Today, I don't have any tanks using one. 

As you can see, I'm not much of a fan of under gravel filters. Many years ago, they were the "only game in town" for biological filtration, so most people used them. Today, there are still people that use them. For myself I don't use them, and can't think of any reason to use one. There are just much better ways to go.


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## oldpunk78 (Nov 1, 2008)

Here it is. Looks like he's deleted the pics though.

http://www.plantedtank.net/forums/diy/78505-rfug-blast-past-diy.html


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## wetworks (Jul 22, 2011)

One other thing to consider is that if you keep plants in this particular tank you will probably have some trouble with roots and whatnot fouling the under-gravel filter plate. Just food for thought.


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## lauraleellbp (Feb 3, 2008)

UGFs and RUGFs fell out of favor mainly because power filters are so much easier to set up and maintain.

They are excellent biofilters, but not very good mechanical filters. And planted tanks need mechanical filtration much more than biological filtration, since the plants themselves are very effective biofilters.

So you can use one if you want to, you'll just have to figure out the best way to add mechanical filtration. And keep plant roots from clogging one up over time.


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## Hoppy (Dec 24, 2005)

Plant roots don't clog up a RFUG because the flow out the tubes under the substrate prevent roots from entering. And, they should have the holes in the tubes facing down, not up, to further inhibit roots from entering. They also don't cause anaerobic bacteria, in fact they help prevent it. A major disadvantage is that they only work well with inert substrates like fine gravel or pool filter sand. Pool filter sand is made for sand bed filters, so it does a great job of mechanical cleaning of the water.

The photos in my DIY write-up were in a different photo storage site from what I now use, and I had to drop the old one since it caused me too many problems. Sorry. I also no longer have those photos, unless I have them on a CD somewhere, which is like storing needles in haystacks.


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