I have had two different emarald crabs I bought for bubble algae, both at separate times. I started missing fish when I added each one. These were blennies if I recall correctly and it was only a 65 gallon tank so they weren't hiding somewhere else. There was also a wrasse who came up with a wound in his side. The crabs, near as I can tell would come upon them at night and kill them, or in the case of the wrasse attempt to kill him. I had never had a problem before adding the crabs or after removing them, just fish started missing a few days after adding them. The first time I banished him to my sump and did some manual removal of the algae. The second time was maybe a month later. I figured I would try again due to the emerald crabs not being known for being fish killers. The second one quickly made it to my sump as well. These were both definitely emerald mithrax crabs as well. One male and one female, I don't remember which was first.
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