My amanos are about as big as my bettas are. They're huge. Echo likes to chase them, but they are too fast for him. Also, there is plenty of plant cover for them to hide in. As soon as they break line of sight, Echo loses interest. Chronos could care less about the shrimp in his tank. I do have a 2.5g RCS tank, but I think I'd be too scared to put them in with bettas. They are much smaller than the Amanos and they are bright red. I'm not sure how well bettas distinguish color, but if they can, I would imagine RCS are like neon-flashing signs for them saying, "EAT ME!"