Under Gravel Filter

[robadk1]

OK... Perhaphs i'm just having some kind of block, But I can't understand UGF's... Maybe it's just because I've never seen one in a tank (My experience is obviously limited to my own two tanks, and the ones at the LFS's and Walmart(Which I pay no attention to for a reason).
Anyway, if someone has the time for a dumb question help me outhere. Diagrams, or just described, anything. Thanks

[rwilliams254]

It's a big plastic thing that sits under the substrate. The intake filter is attached to it. The water passes down through the substrate (i.e. gravel) and into the big plastic thing. Water then travels along the bottom of the tank, then up through the intake tube and into the filter. That's a UGF.


A RUGF is a reverse of that. The return tube is connected to the tube that leads to the big plastic thing under the substrate. Water is then pushed up through the substrate and into the tank.

[robadk1]

Ok, then I guess this is my question, this is why I didn't understand.

If the tube going down into your... black piece under the gravel is only in a corner or maybe two then how does it cover the whole tank? It seems like it would only cover the area around the intake tube going under the gravel.

The intake being in the top left, red being the coverage area...
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And also, i've heard about the air tubes and such for UGF's what's that about?

[rwilliams254]

I don't use one...sorry. However, there are a lot of people here that do use one...I'm sure they will chime in.

[Windy]

UGF are gross because all the debris collects under those plates. The day you chose to switch to an HOB (hang on back) filter and get rid of the UGF, you'll see allll the gunk that the UGF collected.

[robadk1]

Well I don't have one, I currently have two HOB's in my 29 gallon. Does anyone know about the lids they have that have a light and a filter in them, and how do they work, i'm getting a bit off my own topic and i'll probably make a new thread or read some in the equipment section, but if anyone knows offhand, it would be helpfull to me, and anybody else reading this.

[Rbishop]

A lot of misconceptions being posted about UGF..lets try some basic facts...from someone who has operated UGF/RUGF for 30 yrs.

The basic model that comes with the low end style set ups has a plastic plate with small holes or slots. This is placed in the bottom of your tank. There will be collars protruding up, where the clear up lift tubes are inserted and the tubes cut to the appropriate height for your tank and set up. Not all the tubes have to be used, and on those you put caps to block them off.

Next you put in your gravel substrate, 1-2" thick. At the top of the uplift tubes, most have some type of cap that may or may not have carbon in it. This cap has the outlet or return to your tank. It also has a smaller opening for your air line to pass thru.

Most of these will have you push the airline thru the small opening, out the bottom of the cap and connect it to an airstone. Sometimes all of this is accomplished with a rigid tube. You adjust the length of tubing or rigid tube so when the cap is installed, the airstone is just above the collar, and then install the cap. Attach the other end of the airline to an air pump and turn it on. Fill the tank completely up.

You will see a column of bubbles in the air lift tube. These bubbles are displacing water. The end result is that the column of water in the lift tube has less weight than a same sized column of water without the bubbles.

Water outside the lift tube will push down, because of greater weight, and try to get the air lift tube water to the same level. Thus, the flow is water from in your tank pushes down thru the substrate, under the plates and up the lift tubes, and back out into the tank.

The filtration provided is more "biological" filtration than mechanical. Though some large debri may remain in the substrate. There is no more effective means of biological filtration than a UGF. The issue comes from folks not maintaining the UGF correctly by frequent gravel vacs, not overstocking and not overfeeding.

I have never seen a UGF clog or seen the "so called massive debri" under the plates, unless of poor tank maintenance habits. If you run this style of UGF, you should provide some mechanical filtration by means of a HOB or canister.

[Rbishop]

The next step up is to run the UGF with a power head. It will sit on top of the lift tube, which will have to be cut a bit shorter than an air driven set up. The power head will take a suction on the water in the lift tube, causing water in the tank to flow down into and under the plates. The discharge of the powerhead is back out into the tank. The amount of flow increase over a simple air lift methos is tremendous.

But once again, you are achieving just biological filtration and will need something additional for mechanical filtration. The same requirement for good tank practices applies with the need for gravel vacs.

The recent trend has been to make the plates reverse driven. This means forcing water DOWN the lift tubes, under the plates, back up thru the substrate and in to the water column. Once again, this provides biological filtration by passing water that is waste loaded thru the substrate where the bacteria are living and doing the converting. The water moving up, pushes debri out of the gravel and into the water column, where it gets removed by other means. This lightens the need for frequent gravel vacs but doesn't eliminate them.

The force for getting the water down the lift tubes comes from powerheads or canister filter out lets.

[Rbishop]

UGF are gross because all the debris collects under those plates. The day you chose to switch to an HOB (hang on back) filter and get rid of the UGF, you'll see allll the gunk that the UGF collected.

It would only get that "gunk" if you were not maintaining the tank properly.

[Rbishop]

Well I don't have one, I currently have two HOB's in my 29 gallon. Does anyone know about the lids they have that have a light and a filter in them, and how do they work, i'm getting a bit off my own topic and i'll probably make a new thread or read some in the equipment section, but if anyone knows offhand, it would be helpfull to me, and anybody else reading this.
Are you speaking of Eclipse style hoods?

[robadk1]

Wow, Rb. Once again you come through, I just now understand them, that's really cool... I'm very surprised I didn't understand that. One question though, what about that little hole in the top of the outlet of that powerhead?

I guess I dunno, I just saw it on drsfostersmith.com

WOW THANKS.

If anyone doesn't understand UGF's or RUGF's read that.

[Rbishop]

That hole on the powerhead out let, let's you attach some airline tubing that has one end above the water line or connected to an air pump and the other end goes in that hole. Then as water is pumped out into the tank, it entrains some of that air into the water. SOme folks like the look and others don't use it for chemistry reasons with plants and co2. If you are using the powerhead to drive a RUFG, you would not want to do this since it would push lots of air under the plates.

[robadk1]

What about sand, I mean... How do UGF's/RUGF's work around this? And with or without those filters, how do you vac sand?

[Rbishop]

The use of sand with a UGF or RUGF is really kind of self defeating. By the time you get a fine enough netting over the plates so the sand does not fall thru the plates, you decrease the flow thru the plates tremendously.

In a tank with a sand base, the gravel vacs take a bit getting used to. You basically hover the siphon tube close to the sand to entrain the debri, but not so close as to suck up the sand. Takes a little practice, but very acheivable.

[robadk1]

Wow again, thanks alot, and I hope, that i'm not the only one that just learned alot.