I was chatting to someone who mentioned a filtration method that he called reverse filtration. It works thus. You set your tank up with an undergravel filter and an external filter.


An undergravel filter consists of putting an air stone run from an air pump in an upright tube which is connected to a plate with small holes in it. Your gravel sits on top of this. As far as i understand the air bubbles cause a flow of air and water up the tube which causes a flow of water from the main tank area thru the gravel then up the tube and back into the main tank area which allows good bacteria to live in the gravel and thus filter the tank.



Instead of this he suggested putting the outlet of the external filter into the upright of the undergravel filter. Some adaptation may be required to get the right fit. The flow is now supposed to go the opposite way. Down the tube and then up thru the gravel into the main tank area and then into the external filters inlet.

He didnt know if any good bacteria lived in the gravel but he did say that it keeps the gravel very clean and that he rarely has to do anything to the gravel.


If this is the case is would save me a lot of hassle cleaning the gavel


Has anyone heard of this or has any opinions. It should be noted that the bloke only kept small community fish like guppies mollies and not big waste producers (in size and volume) like oscars. I know oscars did but a gravel tidy could be used

Can't I have heard of this filter. Obviously I couldn't comment on how well it works but I don't think there is any way around not cleaning your gravel. The problem is Oscars are very messy and the crap will find itself under the gravel, you've got to clean it. If you don't clean it, that will send the matrix up in your tank and after a while. Yes, there is good bacteria in the gravel but cleaning isn't going to have any adverse affect on your tank as long as you look after the biological filter.

Funny you should mention the air stone. When I clean the filters, you've got to take three trays of media out. Obviously you don't want to leave them out for too long because the bacteria will start dying because there is no oxygen moving through the media. When I thought about doing is putting an air stone in the bottom of the bucket with existing tank water and placing the trays of media on top. I think this would help to keep the bacteria live a little longer and you wouldn't have to worry about rushing to much. Not that I've searched the Internet about this, but I can't see why wouldn't work. Just wondered what you guys think?

I am guessing but if combining an external filter with an undergravel filter keeps the gravel clean it must be because the waste that normally collects in the gravel is blown into the tank and then taken up by the external filter(which would need to be cleaned more often). A lot of the stuff taken out of my oscar tank during a gravel clean is small fine stuff except 'recent' waste. I guess the large waste of oscar breaks up into small bits after a while. This is what appears to happen in my discus tank(sand substrate- easier to see)

This combination of filters may work with a small tank and/or small fish but i am not sure if it would work with oscars and their larger volume of waste. I am tempted to try it as an add on to my tank but i am loathed to spend the time, effort and money if it dont work. I am dreaming of not having to do a gravel clean!!!!!


As for using an air stone when cleaning your filter, are you not being a little bit too fussy. The theory may be good but if things work at the moment then why bother. If too many bacteria were dying due to lack of oxygen then surely this should up in tests for ammonia and nitrite i.e. they would not be zero. If these stay at zero then an air stone in not needed when cleaning the filter. I dont rush to clean my filters but i dont hang around either- the sooner you get it done the sooner you can sit around and watch you fish

I agree, if you're quick, you can normally get it done in time to stop the bacteria dying. However, if you got to remove all the pipework for cleaning, it could be slightly longer.

I bought myself a culander the other day. I think that will make cleaning the media a lot easier. I can believe how filthy one of my filters was the other day. Mind you, I left a little bit longer than I should have.

Not sure about the external canister and the underground filter. Since I've never used an under gravel filter, it is difficult to comment on it. I still think you are going to get some dirt congregating in the gravel which needs to be vacuumed out.

I clean my pipework everytime i clean my filters out. I dont seem to get a problem time wise. The bacteria seem to survive fine. Dont take too long to clean a filter. how long do you think is the max time to clean a filter in ? I have 2 external filters running on each tank an and i clean each one every 6 weeks (3 tanks-one filter a week).


Whats a Culander



If an external filter with undergravel filter significantly reduces my gravel cleaning i will be happy. I currently do half a tank every 3 weeks. I might try this external-undergravel filter a go. when i do i will keep you updated

just be re-reading this post and you said that if you dont clean the gravel it will send the matrix up. What did you mean matrix!

I don't think it takes very long for the bacteria to start dying off, probably around half an hour. It probably does depend on if you let it dry out a little bit as well. I like to keep my nice and wept all the time. However, I don't think a vast amount die off and it doesn't take very long for them to re-establish themselves inside the filtration.

Sorry I am using a speech recognition program which doesn't always get it right if I don't check,. I meant nitrates. Dirty substrate is notorious for sending the nitrate levels up

Im in the clear then. I get my filter and tubes cleaned out in less then half and hour



A good old fashioned typo or that a voice-o

Here's an article about UGF and Reverse UGF too.
Neither it seems work well or are recommended over conventional filters and filtration methods.

www.bestfish.com/ug2.html

I wasnt thinking of using it instead of my normal filtration but as an extra - like an add on to one of my filters. However after reading that link (thank you) i wont bother trying it as it seems it wont cut down on my gravel cleaning. Just dont seem worth spending the money. However if an undergravel filter came my way i would try it just for fun

I think that running UGFs (in either direction of flow) helps to develop biological activity in the gravel, by virtue of the air bubbles passing through it (in reverse mode) or by water being drawn through it in regular mode. Most people don't realize that a deep gravel bed does not help them biologically as it is normally only the surface gravel (top layer) that develops biologically. This is due to the oxygenated water passing over it's surface etc. So, thats being said a UGF should help to get the Biological activity (slightly) deeper into the gravel bed but that does nothing to help keep it dirt and debris free. The gravel will still get dirty and will require vacuuming anyway. Thats because UGFs are not all that consistent with pockets of bubbles here and there or rather good sections of flow and other sections not. Just like an airstone that gets dirty and clogs a bit, you get portions of it with bigger bubbles and portions with no bubbles at all. The air takes the path of least resistance and the same rule applies to UGFs too, in either direction. Doe's it work? Somewhat, but it's "passe" technology and there are today better options...

If you want to "supplement" your exxisting filtration, consider adding a bio wheel to your aqaurium which will greatly increase your biological filtration and is easier and cheaper to maintain. I think the article even mentions using a bio wheel towards the end.