Conduit power is for underwater vision and mining speed, it exist in command. How about you add dolphin's grace in command? I also noticed dolphin's grace wont pop up, it just automatically makes you swim faster when a dolphin is nearby. And also add amplification levels for the effect, like /effect @p dolphins_grace 99999 40 will make you move 40 blocks per second underwater. Hehe im just a huge fan of Aquaman.