Kem Tek 338 vs Jack's Magic Purple Stuff in salt pool?

[PoolDoc]

All the products you mention are HEDP. Kem-Tek is a 20% concentration, but I don't know the concentrations in the Jacks' product. Other than impurities they should be identical . . . IF you can determine concentration.

HEDP was developed by Monsanto as part of their "DeQuest" line. I'm not sure if they still make it; probably most of it is coming from Asia now, as chemical regulations make it extremely difficult to manufacture commodity chemicals profitably here in the US. Asian purities can be suspect, so the question is about quality control, but I doubt you're going to get good answers there.

28 July 2012 update:
HEDP

Jack's Magic Blue Stuff (20% solution)
Jack's Magic Purple Stuff (20% solution)
Jack's Magic Pink Stuff (60% solution)
ProTeam Metal Magic (30% solution)
RamChem Ram Metal Hold ((60% solution? )
Kem-Tek 338-6 Metal & Calcium Eliminator (20% solution)
Haviland Stain & Scale Magic (30% solution? )

Remember, though, manufacturers can change formulations without notice.