I would suspect salt and/or lime scale. It just depends on the specifics of your water chemistry.
Koihaku,
"Acceptable" is far too generic a term. DETAILS, as in real test numbers are needed to even start down the road to a definitive answer
Bardies,
It is likely that you may have naturally elevated salt levels compared to what you are accustomed to. Many of the surface water sources in Oklahoma are naturally on the saline side. Add to that the extensive Oil Well drilling that took place 50-60 years ago (before they knew any better) which unfortunately contaminated many fresh water wells with salt water
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