The train that we used was filter, degas, anion, cation (maybe in the other order, I don't recall), and finally a mixed be polish unit.
The mixed be was backup. We actually ended up using two bottles for one of the ion specific stages (again, I don't recall which) because it would breakthrough first every time.
We had conductivity meters tied to alarms after the C+A step as well as after the mixed bed.
This was a full 2x 100% parallel system, except for the degas.
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P.E. Metallurgy, consulting work welcomed