When you artificially alter your pH, the buffer does not magically shift to sit at the higher pH range. A buffer resists pH change, and once the pH is either artificially increased or decreased, it is susceptible to crashing / reverting back to its preferred range because the buffer zone has been unchanged.
That's the reason coral is used in african tanks to increase the pH. Take it out and the pH will go back down. Put it back in and the water will slowly increase in pH to a certain point as the water is hardened and the base overcomes the buffer.
It is possible to change the buffer range in water, but that requires making your own buffer solution and again, what a pain that is.
Having used the pH altering products in a commercial environment, I would never recommend them to any one. It's a disaster in a bottle.