Decide first if you are going to use plants with roots or not. If not, life is very simple. Anubias, Java fern, Java moss, and obviously anything that floats can be used in a tank with little or no substrate. All you need is enough sand to cover the glass. A depth of 1 cm will be fine, and your catfish will easily keep that clean, with or without the help of snails.
You can buy silver sand at a garden centre (that's what I do) and you'll even find bags of the stuff (e.g. from Tarmac) that is specifically stated to be fish friendly. Obviously, they're ideal. Once you get the sand, clean it well. Empty the tank, pour the sand in, and then add the water by pouring it over something like a plate or a big stone. If you pour the water straight in, it swishes the sand all over the place.
Silica sand is equal in hardness to the glass. This means that if you get grains of sand caught on an algae magnet or some other cleaning device, it will scratch the glass. I use an algae pad (one rather like a plastic brillo-pad) and take care to turn the sponge over with each stroke so that sand grains fall off. Also wipe from top to bottom, so that you don't drag sand from the bottom up the tank. The actual risk is tiny if you do things properly, but the problem with scratches seems to be they are always somewhere really annoying!!!
As well as catfish, some midwater fish, particularly barbs, enjoy rooting about in the sand. On the flip side, because the sand is very bright, some fish feel exposed. Careful use of floating plants as well as bogwood will help to create a sense of shade that these fish will thank you for.
Cheers,
Neale
