Using chemicals to adjust the pH, either up or down, is a bad idea. They cause too much fluctuation. Its far better for a fish to be in pH that is too low or too high than to have fluctuations, which can cause serious health issues and lead to premature death. There are much better ways to adjust it. What is the pH at out of the tap, what are you trying to raise it to, and why?
Please don't use any chemicals to alter your pH - it will hurt your fish in the long run. Besides, as Boxermom said, you'll have to add the chemical to your water with EVERY water change in order to keep it stable ... and that's just so much chemicals in the water. Fish CAN adjust to higher or lower pH ... as long as it changes SLOWLY - that's perfectly fine. BUT ... sudden pH changes (brought about by chemicals added to alter the pH) can definitely mess not only with your water but also with the well-being of your fish. I would NOT recommend doing that Joe.