Hi Pheephee

You mentioned that your tank is a curved one but undergravel filters need not conform to shape of tank. So long as you have approx 70% of yr tank covered should be fine. If you want to be more meticulous, there are loose pieces which you can buy and cut to yr specifications. Plastic pieces don't cost very much anyway.

Since you don't keep any plants, this method combined with yr existing filtration will be excellent in keeping yr water clean and clear. However, if u use the UGF, you'll need to put in small 2-4mm gravel (river sand) 2-3 inches to have an effective bacteria colony. Just remember to clean the gravel (vacumming) once a month (depending on yr stocking level and amount of food u feed). You don't have to strip the UGF unless there are blockages but with regular vacumming, this shouldn't be necessary.

A lot of people condemn the use of UGF, perhaps it's one of the oldest methods of filtration, and fr negative feedback of inexperienced hobbyist. More often than not, these people have never had experience with UGF firsthand!

I've got a 2' tank with UGF and a top filter which gives excellent combi in terms of biological and mechanical filtration. Even after 3 wks of use, and feeding with pellets for my polypterus and clown loaches (usually clouds yr water) my water is still crystal clear. Of course, I use activated carbon. I shall be upgrading to the 4' soon and guess what? I'm still going to maintain the UGF except will prob add another submersible motor on the other end for optimum water flow. This is the level of confidence I have with UGFs!

Apart from that, common sense works a long way; would the aquarium manufacturers continue to produce UGF if they were a failure?