yup. and not a big deal. yes Ive had what i think were negative results with more sensitive corals at a low low ph due to a swing but....7.8 with a dKH of 11 means you probably have high CO2 in your house. I will doubt that a water change will help that long-term. While 7.8 is low, there are reefers that routinely run at that pH. Try opening a window to let some fresh air in the house and see what happens.