3 green barbs in 10g tank...

Lupin

I'd suggest 20g long as minimum for a small group of 6-8 tiger barbs. A 10g is rather cramped.

wendex

If you don't have any luck with your tigers you could get some cherry barbs maybe I've got one male and 2 female (although think more females might be good since he requires a lot of attention!) They don't get 2 big and they're very active all over the tank. I liked them so much when I first got them (they were my very first fish in tank) I was just gonna fill the tank with just cherries.

iamntbatman

Cherry barbs also aren't as demanding about swimming space as tigers, stay smaller and don't require large groups in order to thrive (although the high ratio of females to males that wendex mentioned is definitely a good idea). They also aren't bullies like the tigers, so 1 male and 2 female cherries will leave you room to put other fish in the tank that wouldn't be compatible with the tigers.