Yea dude, the number one thing i tell people on this site is to ditch the Tap water. No one knows what is all in it, yea ppm is helpful, but water is the vehicle that you feed your plants with, the more pure that vehicle, the better the absorption process, the better use of your nutes/water/medium you grow in etc. Everything gets better with good water. Large spikes in pH like that in tap water usually are alarming. I'd assume some sort of bacterium might be growing in your water source. Rememember, we can drink water of much lesser quality than plants can and survive.