triscuit wrote:Good question!
Because the main source of buffering capacity for a home aquarium is bicarbonate. It's cheap, easy, reliable, and has the appropriate dissociation equilibrium to maintain pH where we want it.
Baking soda- NaHCO3 - sodium bicarbonate - alone will stabilize pH at 8.2
Soda ash- Na2CO3 - sodium carbonate - in combination with NaHCO3, pH can stabilize at 9.2
These are the main components of commercial rift lake buffers. There are other buffer systems that can be used, but they will have a larger effect on the nutrient balance. For example, a phosphate buffer will add phosphate to your tank...
Why not use MgSO4 (Epsom salt)? It will add hardness without adding carbonates