Well, I hope I don't confuse you even more....all chelators are sequesterants but not all seqesterants are chelators...chelating compounds have a ring structure (this is just what it sounds like, the atoms are arranged in a ring shape except it is broken and not complete so it can 'clamp' onto the metal ions...sequesterant might or might not have one, but they both will 'deactivate' a metal ion so it does not react with other substances in the water....As far as ascorbic acid...it is actually a reducing agent (this is why vitamin C, ascorbic acid, is referrred to an Anti-Oxidant...the opposite of oxidation is reduction) that changes the oxidation state of metal ions...it does not deactivate them...just makes them dissolve back into solution (It's actually a bit more complicated than that but you really don't want to hear about electron states and orbitals and redox equations ...do you?. (Almost like a line from Wizard of Oz... "electron states and orbitals and redox equations, Oh MY!") Once they have redissolved the sequesterant or chelator added to the water (You did remember to add it, didnt' you?) then deactivates them.

Realize that my explanation is very over simplified but is basically correct. If chem geek or any othe techno geeks care to discuss this with me we can meet in the china shop! This one is for the non technical crowd!