I would love to find a way to tell good vs bad emeralds. I had a big one for a while but he died, I replaced him with a tiny guy until I found him munching and ripping up my Zoas. I wouldn't believe it at first, I saw him in a patch that had been getting smaller so I at first thought something was wrong with them and he was just picking off the hanging ones or maybe eating tiny particles of food, then he proceeded to rip healthy ones off right in front of me! I quickly grabbed my hemostats and yanked him right into my sump. Now the patch is filling in again. BTW he didn't look in the least bit repentant for his evil deed.