If this mineral deposit and build up is calcium carbonate then white vinegar or citric acid will dissolve some of it
It will evervese during contact so don't block it by having all faucet or valves closed
What temperature is your water heater setting?
Higher temperature will form scale in moderately hard water and very quickly in high hardness water
HCl (muriatic acid) will dissolve calcium carbonate easily but must be handled and applied very carefully
Eye and equipment damage can easily occur
Sounds like you have a bad water source and to high water temperature
LSI of any given water determines the scale potential
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