Welcome to NC!
For the hard water use a chelating product regularly - ION swimmers shampoo, Malibu C sachets from Sallys are both sulphate free - and/ or rinse in bottled or boiled water and/ or add a little white vinegar to your rinse water. Product build up including silicones may make your hair behave very strangely on porosity tests, chelating products will usually also clarify off product build up. I suspect if you get your hard water and scalp issues under control you will better see your true curl pattern and properties.
THE NATURAL HAVEN: Junk Science - Hair Porosity Tests / Float or Sink
Is Water Damaging My Hair?
For the scalp issues do you have a formal diagnosis? If not see your family doctor: once you have that we can recommend ingredients or products to work with your scalp and hair. You can easily worsen dermatological issues by self treating. One possibility is your own sebum is contributing to the irritation, in which case your doctor may advise you to cleanse the scalp more frequently than once a week.
Oily scalp can be worsened by sulphate surfactants found in most commercial shampoos, just 1% can thin, dehydrate eve healthy skin sometimes causing it to pump out more oil to protect itself. Shampoos can contain as much as 20%. Other common surfactants can also be highly irritant.
Aqueous Cream : National Eczema Society
THE NATURAL HAVEN: Sulfate Free Shampoos : Least and Most Gentle
An anti inflammatory, nutrient dense diet can benefit many common scalp complaints: it reduces the amount and alters the composition of your sebum, strengthen the skin barrier, calm inappropriate immune responses, reduce irritation/ inflammation.
Heat styling wet hair is pretty damaging, you might investigate heat free methods like wet wrapping. Tangles can also be very damaging because the hairs rub on one another, you might detangle more often than once a month, ideally every time you wash when your hair is slathered in conditioner.
THE NATURAL HAVEN: Heat on Wet Hair = Bubble Hair
THE NATURAL HAVEN: Straightening Facts :How hot is too hot?