Filtration

I wouldn't have UG in my tanks, but then I started keeping fish after they fell out of fashion.

UG filters can work, with certain restrictions. And UG filters with a reverse flow pump are better than standard pumps - that is, it is better for the water to go up through the gravel rather than down as down drags all the fish poo etc into the gravel and onwards to under the plate where it just sits. A reverse flow pump, with a prefilter to catch the bits, gets less messy.

The restrictions:
it is difficult to have plants in the gravel as the roots don't like the water flow, and can cause uneven water flow through the gravel
large decor restricts the water flow
you can't use sand, so can't keep fish that need sand
you can't keep fish that like to dig as they'll move the gravel round and could expose the plates
you shouldn't keep fish classed as messy or they'll cause a lot of mess under the plates
you can't stock as heavily as with an internal or, better still, an external
you are supposed to strip the whole tank down every year to clean it - but you'll know more than me about that
Edit to add to the list that standard UGs are not a good idea if you have fry as they are easily sucked into the gravel


What I have read about is using an external filter as the pump. The outflow from the filter is connected to the UG's tube. This has several benefits -
this acts as a reverse flow pump
it creates an even bigger biofilter
it acts as a prefilter for the UG
you can use other media in the external which you can't with a UG, for instance if you need to use carbon at any time, the external would be the place to put it.



Personally speaking, I would go with an internal or external as they are easier to clean. But if you are happy to work with the restrictions, you can still use a UG