The Chili Rasbora / Boraras Brigittae have very, very tiny mouths and flakes can be squished down some. When you get them they are usually very young/small, and it is wise to feed tiny amounts but several times a day. Like a baby or puppy they do better with a little food more often.
I have used the powdered shrimp food and have used Hikari First Bites fry food, and Hikari Micro Pellets smashed in a bowl with the back of a metal spoon. Also Powered / Freeze dried Daphnia. Frozen defrosted Baby Brine shrimp when they are at least half grown. Cut a slice off of a small cube.
Did you get them yet?
