It's not a ideal situation for sure but what I am pointing out is a possible way to have stable pH so that one does not have to worry about pH/kH drift throughout the week. There are tradeoffs in everything.
You have it backwards, pH and kH don't have to be stable to run a successful healthy tank, but estimating and keeping an appropriate CO2 level is important.
The problem with Seiryu stone is just estimating a proper CO2 rate, once its done and with a decent needle valve the flow rate should remain constant and you don't have to touch it for weeks or months. You may have to reset the equilibrium once the Seiryu stops raising kH if your pH drops too low but that takes a long time.