I recently filled my 75 gallon. My tap water is a 7-7.2pH. I mix 4 gallons of tap with 1 gallon R.O. in a 5 gallon jug. I'm confused because all the water I added had a pH of 6.8, but now it is reading much higher at a 7.8. I haven't added anything other than Prime to the tap water, and my decor are pots, which do not affect my pH. My tank is not cycled or anything. Like I said, I just added the water, and I don't understand how I can have this large pH swing, especially when all the water I added was at a pH of 6.8. Advice anyone?