I just visited the local pool store and was told my CH is too low (160ppm) and adding calcium will keep other chemicals from "wavering" too much. Specifically, the employee said my pH and alkalinity are more likely to "stay put" if the hardness is above 200ppm.
Learning from past mistakes, I refused to purchase calcium before consulting Trouble Free Pool! Just as I suspected, I learned from other threads that vinyl pools don't require calcium.
I'm still perplexed though- has anyone heard of Calcium Hardness affecting other chemical levels? She made it sound like it was a vital stabilizer of sorts.