That's not going to be stable. You're just adding carbonic acid. There's an equilibrium between carbonic acid and dissolved CO2 gas, further affected by air and water temperature and the water's ability to hold dissolved gases. It will air equilibrate over time and go back the way it was.
Just use your pH down and get your hydro pH right around 5.9. This is another example of where re-inventing the wheel is going to make your life harder. It's like the analogy I told you last week about a different issue- if you don't understand the whole mechanism by which a process works, in this case, basic water chemistry, just follow the directions written on the bottle.