Hi thk u 4 your help.
My filter is a Internal power filter model PF3,Tank size approx 82-136 litres.
many thks
ok, that filter is rated at 800 lires per hour, so it's a good fit for your 120L aquarium.
Now here comes ones of the best parts of fish keeping......choosing the fish! Do you have any particular species, types, sizes in mind? Carl's stocking idea above is pretty good, but there are so many variations you could have the choices are almost endless.....from a single species tank, mixed community, adding inverts (snails and shrimps) not to mention the countless fish species, there are lots of things to consider!
I would advise that you start to pull together a little short list of the fish you are interested in and start to research them via the many 'care sheets' that are available on the internet or within this forum. These will give you a pretty good indication of how suitable they are for your tank. Once you have a pretty good idea of what you'd like, come back and run your ideas past the forum again and hopefully you can build a more detailed plan for your tank.
To give you some direction of what you could conside for a 120L here's a VERY ROUGH (there are always exceptions) guide for feasible fish....
tetras, rasborras, gouramis, dwarf cichlids, corydoras, livebearers, puffers (small species), plecos under 6" long.....
you'll find more once you srat digging!