[jer77]

The reason is because of chemicals released by caulerpa irritate most corals including leathers. Most other macroalgae is not really a threat. The other reason is that caulerpa and other macro can easily and quickly overgrow any coral. Zoanthids can also chemically harm passive leather corals, though its not as severe as caulerpa. Zoanthids also multiply quickly and can crowd corals and stunt growth. Unless the zoanthids are growing immediately next to your leathers you should be ok. You should be ok with growing macro too, even caulerpa, as long as you keep it trimmed back from close to your leather corals.