I've had many sharks. You need to take the rainbow shark back to the store or get a larger tank. He's being aggressive because he doesn't have enough room. Rainbow sharks are highly territorial and need more space than the typical one inch per gallon. They will claim a space in the tank and generally leave everyone alone if no one invades their space, but 29 gallons, particularly with the number of fish you have, is too small for your shark to claim a territory. I've had numerous sharks with success in community aquariums, but they need a large tank, with a minimal number of tank mates. Also, he probably killed the SAE because you can't keep other fish with similar body shape or coloration as the rainbow shark.

Z