Bully barbs

I don't know too much about tiger barbs, but I have heard that the more you have the nicer they will be to other species (someone correct me if this is wrong). Maybe you could try adding to your school? Good luck!

 

You need to separate them ASAP. Bullying behaviour as you describe is very serious to the fish picked on, about as bad as it gets second to being chased with a net. It will cause stress that cannot be seen externally until it is too late.

As for the 40 liter (10 gallon) and cories, short term yes but not long-term. As the cories grow they need much more space. But for the time being, I'm sure they would welcome this with gratitude.

My suggestion would be to get rid of the Tiger Barbs, as with the barbs you are seeing the only fish you will ever have in that tank. TB sometimes leave substrate fish alone, but obviously not here, and you have done what you should/could in the group of ten and the tank size. A group of 10-12 in a 30g tank is absolute minimum for TB with no other fish.

However, if you want the TB on their own for the next several years, then getting rid of the cories is the alternative.

 

Minimum here means that anyone intending to have Tiger Barbs needs a group of 10-12 (or more) and this group needs an aquarium of at least 30 gallons. If you want more TB, you could have more in this sized tank, or a larger tank. If you want other species in with the TB, the tank must be larger than the 30g which will only accomodate a group of TB.