no, calcium hardness (actually, the calcium saturation index of which calcium hardness is only one part) only affects how aggressive the water is to plaster surfaces. It does not predict metal corrosion. Low pH is the main water balance parameter that can cause heater damage.
When lowering TA it is best NOT to drop the pH below 7.0 for this reason and also to protect vinyl liners since you cannot know how much lower than 6.8 or 7.0 the pH actually is with the phenol red pH test used for pools.
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