I have a fairly distinct memory of moving a post like that into Speak Easy or Tank Talk from "ID my catfish" which clearly wasn't the right place. But it seems to have gone now. Not sure what happened - if I made some mistake I do appologise.
SA -> South American? Tiger barbs -> Asia!
As to what catfish would be suitable - there are probably about 500 species in the Cat-eLog that would fit in a tank that is around 90 liter. Some would be good candidates to mix with tiger-barbs. Many wouldn't - tiger barbs are well-known for their fin-nipping, particularly if you don't keep a lot of them in one group.
You probably have to narrow it down a little bit as to what you want - and no, saying "Not cory and not pleco" will not really help. Give us a few ideas of what you like.
If you have no idea, use the Cat-eLog search engine to look for fish that match the size (whichever is shorter of 1/4 of the long side of the tank, 1/2 the shortest side of the tank would be a good starting point) and temperature (if you keep the tank temperature stable, input the same for minimum and maximum - the wider range, the fewer fish you get out of it). If you sort the list by "hits", you will get the most popular -> most commonly available [almost always], and thus get some idea of how hard/easy it will be to get one.
www.planetcatfish.com/catelog/search.php
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Mats