Originally Posted by AbbeysDad
I too have used UGF's on and off since the 70's.
I think UGF's are great, but can quickly fail if not setup and serviced properly.
UGF's are a great biological filter but come up short on mechanical, not because they don't do mechanical, but because they do.*
First, the UGF needs 2-3" of medium sized gravel - if the gravel is too coarse, excess food to quickly easily gets pulled under. If the gravel/sand is too fine, water flow gets restricted.
*Like all filters, the (gravel) media requires periodic cleaning to remove debris. This involves a gravel filter used at water changes.
I think where UGF's can fall down and fail for many is that they don't clean the filter and the debris decays and it becomes a nitrate factory.
What I find interesting is the lengths to which some folks go in canister and sumps in order to achieve what they believe is better bio-filtration...when it has been here all along.
I haven't used reverse flow, but see how that can work...but also see it working no better than conventional UGF with regular cleaning.
I tend to challenge the power head theory that more water faster is better. On the other hand, I subscribe to the theory that less (water) is more if/when filtration is better. I think the process works just fine/better with moving highly oxygenated water slowly through the filter bed.
Don't know why you would not favor
(Challenge) powerhead's with reverse flow capabilities(Have you tried it?) In undergravel filtration,
with traditional UG filter,dirt and debrii is pulled down into and under the plate which requires the reg maint you speak of to remove the crud( Anaerobic condition's)) that finds it's way under the plate.
With powerheads capable of reverse flow,, the water is pulled from the aquarium from atop the lift tubes via the powerheads in reverse flow, and water is pushed down and up under and through the plate, and no crud can collect there depending on the GPH rating of powerhead's used.
Does require pre-filter over the intake /output of powerheads assuming you wish for the inner workings of powerhead's to stay cleaner,longer.
Also need canister or HOB filter to clean the water that is being pushed back up through the substrate and once again pushed back down and under the plate. This is /should be,oxygen rich water.
Is very effective filtration for large fishes that produce a lot of waste both while eating,,and excretement. This waste is prevented from gathering on the substrate, down in substrate,/under filter plate, and water turnover is usually sufficient to keep particulates in the water coulmn for afore mentioned canister or HOB filter to clean.Just need to keep mechanical material in filter clean but otherwise,,no more difficult than other filter maint which should be cleaned regularly.