That is an interesting write up on using Seachem Acid Buffer and Alkaline Buffer to arrive at a buffered pH you want. However, as soon as you add CO2 to the water, there is no more buffering than you had when you started. The carbonates are still there in the water, so the CO2 still forms carbonic acid, which reaches an equilibrium value with the carbonate and dissolved CO2. The pH will then be something other than what you buffered it to be. CO2 dissolved in water, carbonic acid, and carbonates form a interrelated group that always affect the pH, buffer or no buffer.
I'm not 100% sure of this, but almost.