You replastered your pool. New plaster releases calcium hydroxide for up to a month. This substance has a pH level of 12, naturally pushing your pH up when absorbed by the water. It weakens your sanitizer. Chlorine sanitizing power is strongest at lower pH levels, so as your pH rises, your water becomes less protected against contaminants like algae. It makes pH harder to adjust. High pH causes high alkalinity ( they’re closely related), and since alkalinity is a pH buffer, this ultimately makes it harder to adjust your pH level. Do not let this chart mislead you. With CYA in your pool, you will still have chlorine, it's just not as pH-dependent because most if it is bound to CYA. More on pH, CYA and chlorine relationships here.

Dry acid ( sodium bisulfate) is a granular acid and a popular alternative for those who aren’t comfortable handling muriatic acid. It’s not uncommon to see your total alkalinity rise over time because pH naturally rises over time, and we know alkalinity always increases with pH.With your pH and alkalinity readings in hand, you can start to figure out the dosage requirements for the muriatic acid. And yes, we are aware we are recommending lower total alkalinity levels than the textbook standards (provided your LSI remains balanced, so keep water temperature in consideration!). The lower alkalinity will allow you to contain pH more effectively. How alkalinity is measured

If you’re using muriatic acid, simply measure the liquid and pour it directly into the deepest area of your pool near an active return jet. Some pool owners prefer to dilute muriatic acid beforehand, but that really isn’t necessary.

What is Total Alkalinity?

The effectiveness of step #4 relies on even distribution of the pH-reducing chemicals in your pool. If your filter isn't working at all, you may want to consult a pool service professional before adding pH reducer. 4. Add pH Reducer to Your Pool