I don't recommend even considering an undergravel filter. Hang on back filters are easier to clean and more flexible (i.e. more choices when it comes to methods of filtration). HOB
filters can have biological, mechanical and chemical filtration while UGF
typically only provide biological filtration (using the gravel bed). UGF
filters require you to dig them up once a year to get all of the mulm that accumulates underneath the filter plates. A lot of the problems with the UGF
can be eliminated by using a powerhead and running it in reverse through the lift tube (this is called a RUGF
) but it still doesn't beat the HOB
for flexibility, effectiveness and ease of use. Get yourself a good AquaClear or Penguin filter and you'll be much better served and so will your fish.