Something eating corals

[Wasabiroot]

Re the heat; water has a high heat capacity. It's likely your tank temp fluctuated less than the air did - it takes a long time for water to match air temp without outside influence. That's why lakes remain cold even when it's warm out in the spring.

 

[PR_nano]

Could be the peppermint or any crab.

I have a scarlet crab that nips coral and recently caught him breaking the spines of my pincushion urchin.