Several years ago, a chemistry student decided to check the color chart that came with bromthymol blue, the indicator pictured in Section 16.6, to make sure that it was accurate enough for measuring the pH in an expensive aquarium. The student put the sensor of a pH meter, known to be accurate, in a small beaker of water and measured the pH at 6.50. He added some bromthymol blue, and the color showed that the solution was fairly acidic, with a pH less than 5. When he rechecked the pH of the solution with the pH meter, it read 4.90. Explain this odd behavior. Does this experiment rule out using bromthymol blue as an indicator in fish tanks?