As far as I know, pH is regulated by the lungs and kidneys. In your blood, pH is represented by C02 + H20 -> H2CO3 -> HCO3- + H+. So, when you exhale rapidly you remove CO2 from your blood....
Parathyroid hormone (PTH) acts to increase serum calcium whereas calcitonin acts to decrease it. However, calcitonin is not usually a significant factor in calcium homeostasis.