Clear Yellow Water
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 discolor the Phenol Red used to test pH. The pH reading looks higher than it actually is, which often causes the mistaken addition of more pH decreaser. The higher the bromine reading, the more tendency to discolor the pH test, so it can become a vicious cycle.
When testing pH for brominated spas, use up to 5 drops of chlorine neutralizer to ensure that you are getting a more accurate reading. When the pH and total alkalinity are properly adjusted, the yellow discoloration should go away.
Note: This information is intended for a residential spa with average use. It is not designed for public, commercial, or semi-public spas. If your hot tub is used more than three times per week, you should check and make chemical additions more often than suggested.