A dying question?

[shimmy]

Ok so last night after hours when my tank should have been sleeping I was up and about. I looked into my tank to see the my fish because i think they are assum, but what i found was the to the most of my surprise. they were all on the bottem DYEING so I freaked out then pulled my self to try to save them. I setup a quick tank out of my bathroom tub and moved them all into it.
the dying question comes from none of them survived.
I tested the tank for everything i have a test for and found nothing wrong.

list of things done yesterday to the tank.
water change
aquascaping


list of lost life.
1 X FoxFace
2 X Clowns
1 X Coral banded shrimp
1 X Emerald Crab
1 X Sally lightfoot
1 X Anthia

What im trying to figure out is what i did wrong to my tank?
What caused them all to die?
Any ideas would be great im afraid to add new fish intill i maybe find out what went wrong.