A mix of pellets(if you can get them to eat them) crickets, earthworms, shrimp, and crayfish, and feederfish. Worked for mine.
By the way, Welcome to MFK Ivan!
rbps are great are they natts or........ does not matter just curious, any pix? as with all rbps verity is the key fresh/ frozen fish , meat of all types fresh/frozen. when small mine ate tetra prima food loved it, then above 8 inches anything and everything ! good luck, best advise large tank as poss always more than three ! powerfull filtration!
i used to feed mine earthworms , beefheart(occasionally) , jumbo prawns,cockles,lancefish, and any non oily fish as it will mess with youre water if its left for to long.