anybody been spraying any cleaning chemicals in the vacinity of the tank, or even anywhere in the room that the tanks in?
how do you top off evap, manually or ato?
what, if anything, do you dose, how much and how often?
do you test for EVERYTHING that you dose?
how much rock do you have in the tank?
do you have a sump, and whats in it?
there are so many things that could've caused this, from an over dose of a single chemical, rapid floccuation of alkalinity or temprature, to accidentally and unknowingly dropping something into the tank. if your rocks were going to leach some toxicchemical into the water it would have likely done it a long time ago. a single snail dieing and rotting away in a 34g tank certainly will not cause this. do you look into your tank very often? if it were because something unknowingly died, you would have noticed changes in the tank that would have qued you off before the crash, i.e. cloudy water or anabnormally heavy and fast spreading algal bloom.
my money is on either some foreign object falling into the tank or an accidental addition of something into the tank too rapidly (namely alkalinity)... not sure about the orange color,but ide imaging that if there was enough rust in the tank to color your skimmate orange everything would probably have slowly withered away in front of your eyes long before the crash.
sorry to hear about it by the way, hope you figure it out...!