What is/was its original pH?
Measure the pH with test strips, often available in a drug store (or fish-tank store).
Sorry, the chem lab that I took regarding converting pH to other concentration-measures was far too long ago.
http://en.wikipedia.org/wiki/Acid%E2%80%93base_titration
The pH value would also increase (acidity decrease) from being associated with more basic compounds placed into the bath.
