My BGK will usually not even acknowledge the other fish unless they are in 'his' cave or when they try to 'share' his bloodworm. Even when he does want someone out of the way - it is usually a 'push' not a bite.
Make sure the tanks mates won't pick on him - they are delicate especially when they are small. Give him multiple hiding spots - and please - no clear plastic tubes - the BGK really do not like them - given any choice at all and they won't use them.
Make sure you place the food 'near' him as he will not come out looking for food until he feels safe in the tank. Many small BGK starve to death as they won't compete for food. Once he feels more secure and the feeding routine is established (left corner of the tank just before bedtime for example) you will see him waiting for you if you are a few minutes late.
There are really only 3 important things to a BGK:
1. good water
2. good food (frozen bloodworm is by far the fav)
3. hiding places where they can turn upside down and sleep - as only a BGK can.
I still target feed my BGK with a set of aquarium gardening tongs. This makes sure he gets a good feeding, I spend time with him and can check to make sure there are no problems, and it reduces the mess of frozen bloodworms being attacked by my Buenos Aires Tetras - they are really messy.
You can teach them to handfeed. I hesitate to put my hands in the water - I don't want to contaiminate the water ( I am also a smoker and don't want to have nicotine addicted fish

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My BGK is now around 11 inches and was under 3 inches when I first bought him. He lives with several Danios, 4 Buenos Aires Tetras, 2 Black skirt tetras, and 4 bronze cories.
Good luck - they are seriously Cool Fish.