PH is affected by many things, and generally speaking water straight out of the tap is a little higher in ph then water that is left to sit out for a day or two... to find out what your waters real PH is leave a glass(non-reactive glass ie pyrex) full of water, then come back and test it when the gases have equalized and the chlorine has evaporated (usually 24-48 hrs). What ever that water tests at is what your tank will generally tend to balance at.
Have you just recently noticed a change to the lower ph or has it been this way all along? If nothing has changed then I suggest not trying to fix something that isnt broke... if it has recently fluxed significatly then I would look into the reason behind the change and not look for the quick fix.(organic matter decaying in the tank, and excess CO2 will significantly lower ph rather rapidly).
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Adam
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