Did your wife take into account of the buffering action of the water? Sometime trying to artificially adjust the pH is like trying to hit a moving target because in an aquarium unlike a lab there are many outside factors and can result in unforeseen consequences.
The most dangerous thing in an aquarist's tool box is a water test kit.
Unless you need some very specific conditions for breeding you are better off just letting the pH fall where ever it does and letting your fish adapt to it. Most fish are very adaptable and can adapt to a really wide range of pH values.
In most river systems pH can change dramatically from precipitation in a matter of minutes to hours.
I agree with everyone about not worrying about the pH, but if you absolutely had to, I would go for some nice tannin leaching wood or peat moss over putting acetic acid in the tank.
