The pH level in spa water should always be between 7.2 and 7.8 and the alkalinity level should be between 80 to 120 parts per million.
Alkalinity is a buffering agent, and its job is to help keep your pH stable.
A Low Alkalinity reading can cause erratic changes in your pH and a high alkalinity can raise your pH level, making it hard to correct.
The pH measures the level of acidity in your water. An improper pH reading can cause you to experience itchy skin, eye irritation and if left uncorrected it quickly deteriorate pillows, spa covers, and eventually your internal spa equipment. So yes, the pH level in your water is the most important thing to constantly check and keep accurate.