The water in your spa should be tested a minimum of twice a week, depending upon your usage of the spa.
The critical test is for pH.
The correct reading is between 7.2 to 7.6.
How to use a chemical test strip (recommended for FL)
You take a strip, and swish it in your spa water for a few seconds. It will start to change color. Compare the color of the strip with the color chart on the bottle that the strips came in.
Adjust the pH, either up or down as determined by the color chart.
If the pH reading is higher than the values listed above, the pH is to be lowered by adding pH decreaser (dry acid), or if the pH is lower than the values listed above, the pH is to be increased by adding pH increaser (soda ash).
Whichever has to be used, they are added at the rate of 1 Tbs/350 gallons of water in the spa. Circulate the water for 1 hour and retest with another test strip. Repeat adding either dry acid or soda ash as needed until the reading for the pH falls between the range of 7.2 – 7.6.
A low pH reading indicates that the water is acidic and will ruin heater elements and seals on your pump. A reading of low pH is more common, as our drinking water is always on the acidic. Another item that will lower the pH is the use of Chlorine or Bromine tablets to sanitize your spa water. They contain Cyneric Acid and that will reduce your pH.
Failure to maintain the proper pH levels as stated above may cause excessive damage to components in contact with the spa water (heater, pump, gaskets).