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View Full Version : How does an undergravel filter work???



toofazt
07-19-2005, 12:34 AM
I was wondering how an undergravle filter works? Is it very efficent? It seems like not too many people have them.

Victor
07-19-2005, 1:44 AM
there's basically a flat panel that sits under your gravel. From that panel there is a tube that runs straight up and is usually connected to a powerhead or something like it. It does what the name says. It's an undergravel filter. It basically takes the debris from under your gravel and sucks it out through that tube that is connected to your powerhead and shoots it out where your other filters will catch the debris.

It's not very efficient and pretty useless. Just vacuum your gravel each time you change your water and you should be fine.

Without it, it's a lot less trouble =)

luvmyfish
07-19-2005, 5:34 AM
Not exactly...what an underground filter does is pull the debris down into your substrate...it does not throw debris into the water. Water changes are just as important when using underground filtration...think of it as rinsing your filters sponge if you will ;) I find them very effecient...and even run one of my tanks with nothing but an undergound filter, and it does beautifully. It does make it way more difficult to clean in the long run, as every 6 mos. or so you have to completely break them down, as they will get very gross underneath eventually and won't work as effeciently. This is sa major hassle. I find that the tanks I have that I use underground in conjuntion with my regular filter do best.

cyberbeer65
07-19-2005, 5:45 AM
Not exactly...what an underground filter does is pull the debris down into your substrate...it does not throw debris into the water. Water changes are just as important when using underground filtration...think of it as rinsing your filters sponge if you will ;) I find them very effecient...and even run one of my tanks with nothing but an undergound filter, and it does beautifully. It does make it way more difficult to clean in the long run, as every 6 mos. or so you have to completely break them down, as they will get very gross underneath eventually and won't work as effeciently. This is sa major hassle. I find that the tanks I have that I use underground in conjuntion with my regular filter do best.

That's way way too much trouble in my opinion.

daveedka
07-19-2005, 7:09 AM
Here we go again.

An undergravel filter is no more work to maintain than any other tank with substrate. It requires good vaccuming, if run in the conventional set up.

If set up in reverse flow it virtually eliminates vaccuming, and works as well or better than any other filter format available.
Either way it would be rediculous to break down your tank to clean the filter. there are much easier much more effective ways even if you slack on maintenance and allow the filter to plug.
On that same note, if you slack on maintenance any filter will plug up eventually, the UGF just plug up slower than most of the others.

An undergravel filter is designed to be a bio-filter not a mechanical filter and it is exceptional at that task. It uses the substrate as an active bacteria bed to create a huge surface area for bio-filtration. They do serve all too well as a mechanical filter and thus create the need for vaccuming, but then there was already a need for vaccuming as it stood.

UGF's are highly effecient, highly effective inexpensive filters that have been given a poor reputation by people who refused to maintain them and then blamed the filter instead of the fishkeeper. If people treated their cannisters as poorly as they did their UGF's cannister would have a bad reputation as well.

Here is an article that covers the basics and also outlines some very good variations to the basic UGF. It is well worht the time it takes to read it.
http://www.aquasource.org/CMS/modules.php?op=modload&name=Sections&file=index&req=viewarticle&artid=17&page=1

Dave

zazz
07-19-2005, 8:16 AM
daveedka already said this, but I Have to chime in.
Undergravel filters work by pulling the WATER through the gravel. It is not their job to remove the debris.
The debris ( poop etc.) gets pulled down into the water along with the water and you have to take that out by vaccuuming the gravel.
The whole gravel bed, with the water constantly moving through it, provides a home for bacteria which process ammonia out of the water.
So, with a regular under gravel filter provides great bio filtration. Also since it pulls the debris down, the water stays very clear looking. The debris HAS to be vacuumed out is all.
How does the filter pull water through the gravel? It can use an air pump, to create an upward flow through the riser tube. this is the original way.
OR you can put a powerhead on top of the riser tube and pull the water up the tube that way.

ALSO
somepeople turn the same equipment into a Reverse Flow Undergravel Filter.(RUGF)
This circulates the water through the gravel also, but instead of puling it down through, it pushes the water up through the gravel.
This keeps the poop from collecting in the gravel. Then you use a Hang on Back filter, or something similar, to remove the floating debris from the water.
( thats the "mechanical " filtration)
I ended up with 'gunk' under my filter plate with my first filter( a regular undergravel run by airpump) because I had never even heard of vacuuming thre gravel. I Did have to break it down and start over, but then with vacuuming every week or so, the filter worked well for the rest of the llfe of the tank.( 2 or 3 years) . That was with Goldfish!

Holly9937
07-19-2005, 9:52 AM
the only reason I don't like them is the look of them. :rolleyes:

daveedka
07-19-2005, 10:36 AM
the only reason I don't like them is the look of them.

That is IMO an acceptaable reason.

Almost every filter format in the hobby has merit, personal preferences are important. I am forbidden by my wife to use anything that has a hose hanging over the back of the tank (due to a siphoning accident some 12 ears ago), so I can't use an external cannister. There are some folks that don't like noise so they don't use HOB's, To each their own.



I ended up with 'gunk' under my filter plate with my first filter( a regular undergravel run by airpump) because I had never even heard of vacuuming thre gravel. I Did have to break it down and start over, but then with vacuuming every week or so, the filter worked well for the rest of the llfe of the tank.( 2 or 3 years) . That was with Goldfish!


Too little information too late I am sure, but next time insert a 1/4" (or bigger if it fits) airline through the riser tube hole and then vaccum under the plates with that. once the majority of the gunk is out, you can influence flow by making thin spots in the substrate (temporarily of course) this will move the mulm around and allow it to flush out.

In all respects except up front price the Reverse flow set-ups are superior. With my planted tanks, vaccuming isn't a good practice, so reverse flow is a must. Aditionally reverse flow provides a good bit of true mechanical filtration via-the intake sponges on the pwerheads.


This circulates the water through the gravel also, but instead of puling it down through, it pushes the water up through the gravel.
This keeps the poop from collecting in the gravel. Then you use a Hang on Back filter, or something similar, to remove the floating debris from the water.


Just an FYI, while the mulm does not collect in the substrate with reverse flow like it does in conventional, the munute particles in the water that do get through the prefilters are still caught in the substrate so the end result is much cleaner substrate but you still get the ultra polished look that many people want in their tanks. Hands down nothing polishes water any better than a UGF or an RFUG. Only diatom filters or micron filters compare and they are of course harder to maintain and more expensive.
Dave

f8ldzz
07-19-2005, 10:39 AM
In all respects except up front price the Reverse flow set-ups are superior. With my planted tanks, vaccuming isn't a good practice, so reverse flow is a must. Aditionally reverse flow provides a good bit of true mechanical filtration via-the intake sponges on the pwerheads.
Don't you just hate repeating yourself so often? :)

RTR
07-19-2005, 10:50 AM
Thanks Dave for hitting all the main points. UG/RFUG are perhaps the most poorly understood filtration technique we use, and are certainly the most poorly maintained. Too many folks feel that out of sight is out of mind, so do no upkeep.

I did many UG/RFUG filters for years, then largely got away from them for a period, but my numbers are going up again (all OE-RFUG), and my tanks are looking (and test) great.

daveedka
07-19-2005, 1:29 PM
Don't you just hate repeating yourself so often?

Some days I do, but then again if one more person learns something valuable then It's a payback for everything others have helped me learn.



I did many UG/RFUG filters for years, then largely got away from them for a period, but my numbers are going up again (all OE-RFUG), and my tanks are looking (and test) great.

With the planted RFUG's I am trying very hard to find a downside. Thus far I cannot find one. The more I study it the more I dount I will ever get away from the RFUG set-ups. My next tank will be RFUG with Flourite, I know rinsing will be a PITA, but with my tap water I think it will be worth the trouble to start out enriched. I am currently running a plastic tub without RFUG where I do my plant grow out and also have some guppies and snails going strong. I can't really see any reason thet the flourite wouldn't work on the RFUG, but time and experimentation will be needed.
Dave

RTR
07-19-2005, 4:35 PM
I have a 50:50 mix of Flourite and conventional gravel planted over OE-RFUG. It was recycled from another planted tank (one of the old plenums) so rinsing was no worse than ordinary used gravel would be. But I do have a rather elaborate gravel wash setup for temperate-weather use. I do need to write that up, but many folks would be rolling on the floor. My feeling are that he who laughs last... ;)

toofazt
07-22-2005, 3:51 AM
1. How do I hook the ugf up so it will be reverse flow undergravel?
2. If I do a rfug then do I ever really need to clean it out at all?
3. How much gravel do should I lay over the rfug filter?
4. If I put my hand on the gravel will I be able to feel water pushing out of the gravel; wouldn't that bother the bottom dwelling fish?
5. Do you find that it evenly spreads out the water flow coming through the gravel, or are some areas of the gravel cleaner than others?
6. I'm assuming that you do a rfug filter useing 2 power heads. What size power heads would I need for a 60gal, a 120gal?


!THANKS!

daveedka
07-22-2005, 8:36 AM
1. How do I hook the ugf up so it will be reverse flow undergravel?
The easiest and IMO the best way is to use penguin powewrheads penguin makes a ready made filter kit for reverse flow, and the powerhead is made to turn around rather than switch motor direction. other systems switch motor direction and that is not as effecient.


2. If I do a rfug then do I ever really need to clean it out at all?
Water changes are still necessary, and light vcaccuming if you don't like the look of mulm laying on top of your substrate. I have two tanks that get no vaccuming whatsoever, and there is usually a light dusting of mulm visible on the gravel.


3. How much gravel do should I lay over the rfug filter?

1" minimum, if you plan to plant you can go as deep as 3"


4. If I put my hand on the gravel will I be able to feel water pushing out of the gravel; wouldn't that bother the bottom dwelling fish?


Nope, there is very little noticable or "felt" current created by a UGF or RFUG set up despite the large water turnover rate.


5. Do you find that it evenly spreads out the water flow coming through the gravel, or are some areas of the gravel cleaner than others?
For the most part the flow is even, decor and plant roots will slow it in some areas, but there is still flow through all parts of the substrate as far as my experiments indicate.


6. I'm assuming that you do a rfug filter useing 2 power heads. What size power heads would I need for a 60gal, a 120gal?
I personally run a bit more flow than most Foks do. For a 60g I would run two penguin 1140's, most folks would probably run two penguin 660's. For a 120g I would run 4-6 1140's depending on tank dimensions. my 115g is a 48"x18" tank and has 4 1140's running on it. Higher flow definately runs better IMO and IME but low flow works well enough. The more motors you submerge in a tank, the more heat is created. at some point you have too much heat and you run into warmer water than you may want to have. additionally if you run other internal filters as RTR often does you have less margin for bigger powerheads. In my case, I run mostly HOB's which don't have the side effect of adding heat. Right now MY 115 runs 4 1140 pengiuns on the RFUG, 1 550 pengiun on the co2 reactor, and two additional powerheads (I forget model and size) for current. it also has an eheim aquaball filter running in the tank, and I have yet to see heat issues. In smaller tanks the heat becomes more of a side effect with high flow. I haven't yet put together watts of motor per gallon type specs to give you any real guidelines on where the limits might be.
dave

zazz
07-22-2005, 9:31 AM
Too little information too late I am sure, but next time insert a 1/4" (or bigger if it fits) airline through the riser tube hole and then vaccum under the plates with that. once the majority of the gunk is out, you can influence flow by making thin spots in the substrate (temporarily of course) this will move the mulm around and allow it to flush out.

Thank you! Not entirely too late as I am starting a new tank with ugf.


In all respects except up front price the Reverse flow set-ups are superior. With my planted tanks, vaccuming isn't a good practice, so reverse flow is a must. Aditionally reverse flow provides a good bit of true mechanical filtration via-the intake sponges on the pwerheads.

Just an FYI, while the mulm does not collect in the substrate with reverse flow like it does in conventional, the munute particles in the water that do get through the prefilters are still caught in the substrate so the end result is much cleaner substrate but you still get the ultra polished look that many people want in their tanks. Hands down nothing polishes water any better than a UGF or an RFUG. Only diatom filters or micron filters compare and they are of course harder to maintain and more expensive.
Dave
Two things that I hadn't realized. Obviously I have only read about, not used a reverse flow under gravel. Sorry if I was misleading in earlier post.
Your answers to toofazts enumerated questions were helpful to me as well.

FishSeller
07-22-2005, 9:43 AM
With RUGF in a planted tank, you also eliminate the need for substrate cable heaters as heated water is being physically pumped through the gravel. I've never used one personally, but I definately see the advantages of this set-up. With RUGF, are "dead spots" in the filter still an issue the way they are in a regular UGF?

RTR
07-22-2005, 10:03 AM
I am one of the folks with over-heating problems. I massively over-filter all of my tanks, and my house/ambient temps are very stable and tightly controlled. I have not needed heaters since we built this place, but the other side of the same coin is that my tanks run a bit warmer than I would like. The last planted RFUG I set has two Penguin 1140 powerheads driving a 29 gallon RFUG, plus two old Fluval 2 (not the "improved" 2a) internal canisters for extra mechanical and current. The tank ran over 82F all the time, so I set a small fan under the tank (one of my few stands with a viewable tank base) which dropped the tank temp a couple of degrees.

I'd like to reset the 55 in the same room planted RFUG, but I know it would be worse, as its internals are Eheims, a bit larger and a bit more wattage than the old Fluvals, plus it has a bit higher lighting/gallon (more heat input). I hate going to Eheim external canisters for the extra mechanical, as they are not as user friendly (easy) to rinse on a weekly basis. I'm still waffling on that one.

janderson
07-22-2005, 1:22 PM
in order to convert from UG to RFUG, is a reverse-flow capable powerheads (like the Penguin 660R) all you need or are there any other parts necessary :confused: ?

Thanks.

daveedka
07-22-2005, 1:42 PM
In the case of the 660 R it is the 660 powerhead complete with the reverse flow sponge kit, so it is all you would need.
If buying other models of penguin powerheads, or if you already own a 660 then you simply need to purchase the reverse flow sponge kit. The kit comes with everything you need to set up any penguin powerhead in reverse flow configuration.

There are some other brands that have reversable powerheads, rather than making it easy to actually turn the powerhead around. Reversable pumps are never as good backwards as they are forward so these lack some appeal IMO.

With any reverse flow set-up the real key is to make sure there is a filter of some kind to prevent the mulm from getting pumped under the plates in high volume. This can be a DIY project or you can go with ready made parts like the penguin kit. To me the penguins are extremely economical and dependable for the money, and the ready made reverse flow sponge kit is simple and inexpensive.
Dave

Joele
07-24-2005, 12:06 AM
Thanks daveedka for defending the UGF LOL, I was horrified reading some of the earlier posts slamming it but obviously due to a misunderstanding of how it works...

I am new to this forum although not new to aquaria (although I have been in marine for the last 5 years) recently getting back into freshwater, and went with an UGF... I always preferred undergravel to those HOF, I had tried them on various tanks but always prefered the UGF.

I don't use Reverse Flow I use a standard UGF and had one running for 4 years before I had to break the tank down (due to moving house) and it wasn't clogged up at all, although my nana had a healthy root system under there... It is far from true to say you need to pull your tank apart each year... A 4 weekly gravel vacumn was my UGF maintanence technique... Although one thing I would point out I would tended to give a good vacumn of just one side of the tank each 4 week cycle (alternating each time)...

RTR
07-24-2005, 6:06 PM
Joele - even the alternate area vacuuming is not required. If the filter is well maintained and not loaded with mulm, all of the beneficial bacteria will be substrate attached and will not be pulled off by vacuuming. If they could be pulled off easily, fluidized bed filters which are essentially vacuumed 24/7/365 would not work, and they do work.

Joele
07-24-2005, 8:15 PM
Joele - even the alternate area vacuuming is not required. If the filter is well maintained and not loaded with mulm, all of the beneficial bacteria will be substrate attached and will not be pulled off by vacuuming. If they could be pulled off easily, fluidized bed filters which are essentially vacuumed 24/7/365 would not work, and they do work.

Ohh well I doubt it hurt ;-) but what you say makes sense, thanks for the tip...

lions_07
02-09-2006, 1:26 AM
I only have a 10 gallon tank and am rather knew to this.......so sorry if this is a stupid question......i'd just appreciate some help. I have a ugf and an air-pump, now from what i have read a rugf is much better and i was wondering if i could convert my rugf with just my air-pump, or would i need to get the power-heads?

OrionGirl
02-09-2006, 9:43 AM
You need to use powerheads to go reverse flow--with just air, there's no way to force the water the other direction.

Shelzbells
02-09-2006, 10:13 AM
Excellant info you guys, I have used UGF's from day one and have always had excellant results with them. I do use other types of filters on some of my other tanks, but the ugf has to be my fave.


Too little information too late I am sure, but next time insert a 1/4" (or bigger if it fits) airline through the riser tube hole and then vaccum under the plates with that. once the majority of the gunk is out, you can influence flow by making thin spots in the substrate (temporarily of course) this will move the mulm around and allow it to flush out.Dave

Like Dave said, there are ways to manipulate the debris under the filter, to make it easier to vacuum it all out.

Great tip there!!!

TDWagner
02-17-2006, 11:09 AM
I have both UGF and an Emperor 400 HOB on my 55g.

When converting to RUGF, should the intake of the HOB be moved further up, or left at the bottom (1-2 inches above the substrate)?

I'm wondering if the reverse flow will suspend debris higher up in the tank, in which case it would make more sense for the intake to be at the mid-water level rather then the bottom to be most efficient at mechanical filtration.

TIA!!

fish_breeder_05
02-17-2006, 11:19 AM
but a power head is pretty useful. my yoyo,and dogo loach love to swim aginst the stream, and for some fish like glass catfish, a strong stream is required

mduros
02-17-2006, 12:42 PM
Thanks for all of the good UGF info folks. I have always used them. My brother was a marine biologist and used them, and taught me to use them as a little girl. I never gave it a second thought until I read here or somewhere that it was antiquated technology. Unfortunately, my big brother is no longer with me to ask. Anyhow, I have dabbled with HOB filters since, but I still think my undergravels are wonderful, they've never failed me. So thanks.
Take care,
Mary.

RTR
02-18-2006, 1:05 PM
Many folks have been damaged by UG filtration because they were not taught how to maintain them. An ignored UG is a time bomb. But so can an ignored HOB or canister filter be such, or simply under-maintained substrate can do the same. All tank components require care - if properly handled, all formats of filtration can do the job. Improperly handled, all can be major problems.

I love the folks who claim that UG is antiquted tech - Canisters, power filters, and UG all came in about the same time (I was in the hobby already then). Wet/Dry filters popularity came later, fluidized beds later still. All the first three were based on changes in the pumps available to the hobbyist. All have developed technically. UG has been the most misused and misunderstood, and unfortunately it still is.