I just added this to my chronicle, but think it needs to be added to this list too..
This wasn't my mistake or my tank, but though I'd share.
My friend here in town was moving his 75g SW tank out of the living room. To do so, he was filling all of 10 culligan jugs and some rubbermaid bins with the current water, to just add again after it's moved. He got all of the jugs filled, and the tank moved.
Started to add the jugs back to the tank. On the second to last one, he added it, and the fish instantly croaked. Along with all inverts, and corals dimished within minutes.
He was freaking out, calling me asking what he'd done. I asked him what else has been in the culligan jugs, he said ONLY tank water! So, I got off of the phone with him, he walked back to the tank and there were bubble/suds pouring out of his skimmer, and building higher on the surface of the tank by the second.
He called his wife to ask what could've happened. She remembered---she forgot to tell him she used one of the Culligan jugs the week prior to mix their carpet shampoo in and forgot to mark which one.....
Needless to say, this was 10 days ago. You will never believe or you will, lol what survived. ALL of his GSP survived and doing great.
Lesson learned, don't let wife use Culligan jugs...