Trashing on the idiot that did this is not only appropriate it is right. If someone invited to your home nailed your cat to your front door as a joke would you not suggest that person behaved inappropriately and should be punished and/or excoriated from your group of future houseguests? ...Wake Up!
I'm willing to bet this wasn't a person that is usually in their close circle of friends, as such person would know not to be such a careless ****wad, and would know that said poster cares about their fish. That person would never be welcome in my house again (and I would file a police report that the person vandalized my home if doing so wouldn't cause strife among people I knew).
That being said, good luck with your fish... I know oils can cause respiratory problems in fish. If it was my tank I would be doing water changes as much as possible.