Spa water that is tinted clear yellow usually indicates a high bromine residual and a low pH. This is fairly common with bromine spa systems, because the bromine can discolour the Phenol Red used to test pH (“bromophenol blue”). The pH reading looks higher than it actually is, which often causes the mistaken addition of more acid. The higher the bromine reading, the more tendency to discolour the pH test, so it can become a vicious cycle.
When testing pH for brominated spas, use up to 5 drops of chlorine neutraliser to ensure that you are getting a more accurate reading. When the pH and total alkalinity are properly adjusted, the yellow discolouration should go away.
