Expert Insight

• If the water isn't properly treated, public hot tubs can facilitate the growth and spread of germs. The Centers for Disease Control recommends that hot tub owners keep pH between 7.2 and 7.8; these levels provide for sufficient chlorine or bromine activity while avoiding corrosion. If you're having trouble keeping the pH in this range, however, there are several steps you can take to restore optimal pH.
  
  

Function

• Adding muriatic acid or sodium bisulfate will reduce the pH of your hot tub water. It's essential to bear in mind, however, that muriatic acid is a strong acid, so you should only add extremely small quantities, otherwise you will overshoot the mark, and reduce the pH too far. Always wear rubber gloves and safety glasses when working with muriatic acid, and never bring it in contact with your skin. Soda ash or sodium carbonate will raise the pH; again, however, the amount you'll need should be fairly small. Add these chemicals in small increments, and test the pH as you do so, to avoid adding too much.
  
  

Considerations

• Total alkalinity measures the ability of your hot tub water to resist change in pH, and hence, the stability of the pH level. The Michigan State University pool chemistry guide recommends that you maintain total alkalinity in the 80 to 125 parts per million range. Adding sodium bicarbonate will increase total alkalinity, although again, it's important to add only small quantities and test while adding it to avoid adding too much. Regularly changing the hot tub water is helpful; it's also a good idea to run the hot tub at lower temperatures, since at high temperatures, calcium carbonate is less soluble, and as the calcium carbonate in the water precipitates, it can form scale and affect the stability of the pH.