How big is the tank?
Most barbs are shoaling fish like tetras and rasboras, if you only have one or two they are much more likely to get very nippy.
If you like barbs - cherry barbs are much smaller, completely peaceful and should be kept in pairs anyway

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Your zebra loach could probably use some friends too, keeping just one isn't really too fair as they are also shoaling fish and like to interact and 'play' with each other a lot.
It would be better to bump up the number of rasboras too, but tbh you can probably get away without doing that if they seem happy (active and not hiding behind things/back of tank or being nippy).