Cow fish help

[Coleus]

my experience with cow fish poisonous is when i bought a cow fish and emperor angel at the same time and then put them in a bucket and acclimate them. 30 minutes later, i found my emperor angel is dead so i was scare to put the cow fish in to my main tank. So I put air pump into the bucket and set up a quarantine tank for cow fish. 1 hour later, found it dead also with the white stuff in the water.