Don't bother checking the pH of RO water. It has no alkalinity, so the pH will swing wildly. Usually the pH of RO water will climb very high like that if the water is agitated, as oxygen mixes into the water. Even using a dropper to extract a test amount is enough to do this. Mixing salt into it adds alkalinity and stabilizes the pH.
Long story short, you can't really measure the pH or pure RO water.