What To Do With Undergravel Filter?!?!?!?!?!

[dave_oddballs]

on my fluval roma 240 litre tank i have a fluval fx5 and a 4 ft undergravel filter plate with a 480 lph aquaclear powerhead at each end. when i come to do water changes and syphon / vac the gravel there seems to be a build up of 'matter' about 20 mm under the surface. i have read in some places that undergravel filters cause more harm than good, i am unsure about this and tend to work off my own initiative and from experience. the undergravel filter was obviously put there with good intentions and because i have some large and messy fish i thought it would help break down waste that rested on the gravel. i know for a fact the fx5 is more than capable of filtering more than4 times the volume of my tank so it should stay clean all the time as i regularly maintain it. my instinct is that the undergravel filter sucks waste and matter halfway through the gravel then it sits there, which would be why i find loads of materiel when i clean which forms an almost grey mat under the gravel, and released dirt, waste and ammonia back into my tank constantly, which is obviously not good, i am wanting to make a decision today and remove it if needs be so any info asap would be greatly appreciated
Dave

 

[Colin_T]

Undergravel (U/G) filters do trap gunk in the substrate but they also hold good bacteria that break down ammonia in to nitrite and then nitrate. If you gravel clean the tank each week, then you will remove most of the gunk and keep the gravel clean. This allows the U/G filter to work efficiently and when maintained properly, they are a very good filter due to the large surface area they have.
If you leave undergravel filter uncleaned (no gravel cleaning) then they block up and cause problems. Also if you have big rocks resting on the gravel it will prevent the water flowing through the gravel and this will stop it working in that particular area.

When using a gravel cleaner on the U/G filter you should push the gravel cleaner into the substrate and leave it there until the water coming out is clean. Then lift the gravel cleaner up and move it to another spot.

Sediment and gunk will always settle into the substrate regardless of it you have an undergravel filter or not.