When people buy Oscars,it is usually an impulse buy and they are taken home to grow quickly and eat all of the other fish in the tank. It may be some time before it is apparent that they are no ordinary fish and that a bigger tank with better filtration is required. At this point it should be decided what sort of filtration ,tank size etc is required. filtration often takes the course of external power filters which provide a fast flow of water filtering the water in the tank at least once an hour, but using the external filter still doesn't give us a great deal of media to filter the water. One way of getting a large area of biological filtration is to use the gravel on the bottom of the tank as a biological filter. If a depth of 3 inches of gravel can be used as a biological filter this will give a huge amount of media compared to that in the external filter. But how can we use the gravel at the bottom to aid our filtration? quite simple,return to the days when we all used undergravel filters but with a slight difference. We connect up the ug filter to an external power filter and run it in reverse flow instead of the conventional flow with power heads. An under gravel filter works quite simply by displacing the water from underneath the gravel up the uplift tubes and out into the tank. The water then is drawn down through the gravel to replace that which was sucked up the uplift tube. The action of drawing the water through the gravel creates a flow and as bacteria build up in the gravel it will filter the water as it flows through. The problem with undergravel filters is that over time the rubbish gets trapped in the gravel and eventually blocks it rendering it useless. That's where reverse flow comes into its own. By blowing water down the uplift tubes we are then blowing water up through the gravel creating a flow of water through the gravel but in the opposite direction this effectively stops detritus from settling on the floor of the aquarium and then the ug filter cannot become clogged up. For this system you will need:
an Undergravel filter to fit your tank
2-3 inches of gravel
gravel tidy
silicone sealer
external power filter
to set up
First, the night before you intend to set up, silicone the external filter outlet pipe into the uplift tube, pushing the pipe to the bottom of the tube.
The next day you can place the undergravel filter and the uplift tube with the hose,in the tank and add 1-1.5 inches of gravel which you can smooth out.
Then add the gravel tidy and the rest of the gravel on top of the gravel tidy.(This is placed on the gravel to prevent the Oscars from digging down to the ug filter).
Now slowly add your water and place the inlet pipe for the external filter.
Once the tank is full you can start the filter and wait two - three weeks for your filter to mature. It will take some time before your gravel seeds with bacteria but when it does you will have a huge biological filter.( see the diagram below)
NB this can only be used with gravel substrates it will not work with sand.

Very nice article dinger454.

I had a discussion on here before about this (subject was 'reverse filtration'. My idea was that this would reduce the amount of gravel cleaning needed. However i was told that large waste wouldnt be removed and would sit on the gravel and block it up unless you regularly did a gravel clean, yet you say this wouldnt be the case. Have you used this before and did the UG ever block up and how often do you clean the gravel

I have used this method before to great success,all but the largest pieces of muck are left suspended in the water and are drawn into the power filter. I did sometimes clean the bottom of the tank but no where near as much as with normal filtration.This system would not become clogged like ordinary ug filtration. Once every six months i cleaned the underneath of the gravel by connecting up the filter the other way and pumping the water through the filter and straight into a bucket i then cleaned the filter out before connecting it back up the right way. The only problem i had with this method was priming the external filter which i did with an extra piece of pipe.This method does require you to keep an eye on the filter so that it does not become clogged i would suggest checking it every couple of weeks. I would recommend this set up as a new set up and would discourage form trying to change a system that is already set up.

I can see the problem of priming the filter, you need the outlet out of the water

Why do you discourage existing set ups from going over to this?

Also with a new set up on this system could you get away with have less external filtration compared without out the UGF or would you always recommend it as an addition?

Does muck settle under rocks and wood or does it clear that too

You should see an improvement on muck all around the tank. I would still recomend you keep all of the media in the external but if you could afford it you could have an extra external just to hook up to the reverse flow with no media at all. you could also run an internal hooked up with no media in it to increase flow providing you have got the external filter as well. I should have made it a bit clearer what i meant about not changing a current set up to reverse flow is changing an existing conventional ug filter to reverse whilst the tank is running. Maybe thats a bit obvious though