You can set up two tanks side-by-side, with everything being the same....rock source, water, salt mix, lights, etc, and they will almost always turn out biologically different.
And you were correct in not adding anything..... a stable tank is a happy tank. A pH of 8.0 is a little lower than normal, but not bad. Using buffers & bouncing the pH up & down could be detrimental.
Wanna calculate the cost of that new reef tank?? Take your worst nightmare, double it, and you're halfway there.