Under Gravel Filters

[Meeksworth]

I'm setting up a new tank and I intend to add an undergravel filter for additional filtration along with my power filter.
I'm skeptical about how well they work though. I have read conflicting opinions. Some have said that they don't work well for biological or mechanical filtration while I have also heard that they are good for bio filtration.

I personally would like for it to add more bio filtration. I don't intend to use it for mechanical filtration at all. I was also hoping that the flow through the gravel would prevent me for having to vacuum quite as much.

Can anyone attest or provide evidence one way or another?

 

[daz4321]

They worked well enough for years before we had externals and no you will have to vacuum more as you will be sucking the dirt into the gravel.

 

[fluttermoth]

If you're going to be running 'power' filtration as well, had you thought about a reverse flow system? Needs (obviously!) less maintenance than the 'traditional' type of UG.

 

[TwoTankAmin]

To date nobody has designed a better bio filter than an undergravel filter. The reason is simple, the entire gravel bed becomes the bio media. And there is no way to have that much surface available in almost any other feasible type of tank filter. However, there is one big caveat to that statement. You must set it up and maintain it properly.

First, the gravel must be a mid/medium sized stone. Too small and the flow through will not be suffcient, too large and it will be too great and the potential surface area will be reduced. Second, you need to have a bed close to 3 inches deep, too shallow and it reduces the effectiveness.

The initial ugf pulled water down though the gravel using and upflow generated by rising bubbles in an uplift tube (the same process that makes sponge filters work). However, a better way was found called a reverse undergravel filter (rugf). One can invert the flow by using a powerhead. Water is forced down the uplift tube and then out up through the gravel. This design change offered several benefits.

Because the water flows up through the gravel, much of the solids that would normally work their way into the gravel, either from gravity or from the downward sucking of the traditional ugf, are now blown back up into the water. To prevent the solids from being sucked into the powerhead, you use an intake sponge. You then add a second filter, usually a power filter, which is loaded primarily for mechanical waste removal. So now all the solids kept floating are sucked out of the water. And this means you will actually need to vacuum less often. Plus, the power filter can also be used to hold carbon or other chemical media when needed. The power filter also serves to agitate the surface so O can enter and co2 can exit. Finally, you must rinse out the intake sponge on the powerhead weekly.

This filter arrangement is not good to use in certain type tanks however. Tanks with fish that like to dig big time and most planted tanks- attaching plants to wood and rocks works fine but many plants that need to be in substrate may not, especially ones you can't plant in medium size gravel.

The final thing to realize about undergravel filters is that when you put a rock or a piece of wood etc. on the gravel, you impede the flow through it. So there is a limit to how much stuff you can put on the gravel before it becomes a detriment.

What made me give up my rugf was spotting swordtail and panda cory fry under the plate.

 

[DrRob]

Why not go for a hamburg filter, if all you want is biological?

 

[Meeksworth]

Now that I know about RUGFs they seem like a great idea. In fact I've already bought and put in he ugf. I still need to get the power head though. @ DrRob I haven't considered a Hamburg be aide I have no idea what that is.

 

[DrRob]

It's one of these.

http/www.janrigter.nl/mattenfilter/