I really have to agree with RTR here..mostly because of the activeness of Tiger barbs more so than the potential size. There are many fish that grow to the size of Tiger barbs(ie. dwarf gouramis), but don't have near the energy level. Tiger barbs like to 'run' so to speak...and need plenty of room to do so. It's akin to keeping certain breeds of dogs, some are much more active than others and need a big back yard. I think your barbs are fine in the 10g as of now at their current size, but if you plan to keep them for awhile, it would be better if they were moved to larger quarters as soon as they reach the 1 1/4" - 1 1/2" size. Personally, I wouldn't keep them in any tank under 36". A great alternative to tiger barbs in a 10g would be a school of Rasboras, instead.