Those are most likely hermit crab larvae. They look like mysids but behave and swim differently. Mysis usually swims head forward while shrimp and crab larvae usually drift or swim rather tail first. Also, the abrupt swimming pattern fits hermit crab larvae. Also, the reef Mysids you find in our tanks usually stay on the ground and in the corners and rarely get into the water column like larvae.They're so small! This was the best I could do for pics. Tbh I think they're too small to be clownfish fry but idk for sure