Sorry to hear about your problems. If I see trouble, I immediately see where my temperature, salinity, nitrite, nitrate and ammonia are! What are your parameters in both of your tanks? You should have added those details. Also, I have had Zoas just melt away on me before for no apparent reason. Emerald crab? Nope, I don't do crabs(some people say that emeralds turn into little monsters). When I do have bubble algae, it just disappears on its own to be honest. Problems with a reef tank? We all have encountered problems here and there. I have even had tank crashes on me where everything dies! Recently, I had a febreeze incident where most of my SPS died in my fusion 10G. I would move your Zoas further down the rock work too see if that helps them and I would get rid of that little monster ASAP. Peppermint shrimp also eats corals!The only inverts I tolerate in my tanks are cleaner shrimp, candy pistol shrimp and hermits that don't get too big. Do you have a toadstool in there? I have never liked those, because if it dies, it could wipe out your tank completely. Good luck with your problems. I would do a 50% or more water change to be on the safe side.

Emerald Crabs will eat anything! Once they run out of algae, its all game. I hope this isn't the case with your. It is something to look out for though. Best of luck brother. Tank look awesome.