I moved this to a new thread.
You will ALWAYS get faster attention with a new thread than attaching to something like the Chemsitry Question of the Day since I might not check it at all for a day or more since it isn't requiring responses.
So as to the pH, I think pH 7.4 is unlikely to be accurate unless the alkalinity is very low, but can you describe the tank?
Is it a reef tank?
Have you measured the alkalinity?
How are you measuring pH?
Do not do a knew jerk buffering response as it may make things worse if the measurement is an error or alkalinity is already OK.
What sort of distress from the fish?