I have super hard water (14+gH) at work and 8gH at home (ph at both places is 8 out of the tap) and I haven't noticed any difference in the plants that couldn't be attributed to other factors. But I only grow hardy low-tech plants with Excel and no Co2 so I suspect you might notice a difference with more demanding plants. I have various crypts, mosses, rotala rotundifolia, amazon frogbit, marsilea minuta, hydrocotyle tripartita, hygro, and of course anubias. Those are my work plants and they grow fine. So I wouldn't worry so much about pH unless EVERY other factor (light, CO2, ferts) is optimal and you're still having issues.