by macro I would guess you mean caulerpa algae, this algae is problematic. it goes sexual and breaks down flooding the tank with toxins and the stored up trates & phos. you would prune when new growth is about 8" long and you can remove up to 1/2. amount to prune depends on how much you feel you need. when possible old growth is removed rather than new. if you pinch the stems tween your index finger and thumb nail there will be no bleeding.there are better choices than caulerpa. ie chatomorpha,graceleria, ulva etc. they do not go sexual and not as growth rampant. they are pruned much the same way.