There are three signs: You're adding too many hot tub chemicals If you notice itchy skin, red or irritated eyes, or flaky scale buildup on your hot tub surfaces, it means your water chemistry is out of balance test and balance your water once a week. Start by adjusting your alkalinity and pH first, then balance your sanitizer like chlorine or bromine. It's actually an imbalance of alkalinity and pH that irritates your skin and eyes and causes scale to build up. But your sanitizer levels need to be in range as well to keep harmful bacteria and algae at Bay.