CichlidAndrew said:
Okay for gravel but cannot be used with sand. I think it is more beneficial to have under gravel jets instead imo.
Actually, a least one major vendor uses under-sand filtration quite sucessfully...
http://www.ohiexchange.com/armke/forget_the_fish.html
demonsoni said:
ugf's are so 10 years ago.
Heh, and they work just as well today as they did 10 years ago. You'd be hard pressed to find a commercial filter that gives the same "bang for your buck", and even most DIY solutions are going to be hard pressed to compete on a per-dollar basis.
The disadvantage is that they're more labor intensive. 10 years ago we didn't have good alternatives, and the UGF worked just fine, so it was standard. We aquarists being the lazy folk that we are, we're all for paying more money to do less work

. Or for DIY folks, doing more work to pay less money to do less work.
UGF's are easy and cheap to set up, but they require a disciplined gravel vacuuming schedule. If you don't maintain your UGF then you can eventually reach a bugaboo with tons of gunk underneath it that turns into a "Nitrate Factory" but lets be honest -- if you have UGJ's (UGJets, not to be confused with UGFilters) and cannister filters, all that "gunk" is going to end up in your cannister filter and you have just as bad (or worse) a "Nitrate Factory" until you clean it out.
Now that said, I do believe there are times when a UGF is not appropriate (or at least not without taking extra steps) -- and that's when you've got fish that dig. My N. Multifasciatus dug a big pit until glass was exposed (and they kept digging even then, but it didn't get any deeper). That would do bad things to your UGF. There are ways around it, of course, such as putting a barrier halfway through the sand/gravel to prevent them from exposing the UGF plate, but imho at that point you might want to seriously consider alternate forms of filtration.
Any way you cut it -- it's your money, and your elbow grease. Choose how much of the one you're willing to spend, and apply the other in inverse proportion

.
-Rick (the armchair aquarist, who being one of those crazy DIY folks is making a wet/dry filter for his 29 gallon tank, but by the time it's all said and done he will have spent enough for a mid-sized classic Eheim. That wouldn't have been nearly as satisfying though

)