When the pH is really low, adding baking soda has a big impact on the pH because it depends on how much of the bicarbonate converts to carbon dioxide.
The below graph shows how much the pH is impacted by adding baking soda because it shows how much gets converted to carbon dioxide.
The reference to little effect is when the pH is over 7.5, but you don't need to raise the pH in that case anyway.
Anytime you need to raise the pH, baking soda will work.
I would never use sodium carbonate (pH increaser aka soda ash).
This shows how much of the added baking soda stays as baking soda and the rest converts into carbonic acid/dissolved carbon dioxide.
All baking soda (Hydrogen carbonate) that picks up a hydrogen ion increases the pH.
Baking soda only has a small effect on the pH when the pH is already high because only a tiny amount of baking soda converts to carbonic acid when the pH is high.
HCO
3- + H
+ --> H
2CO
3 --> H
2O + CO
2
pH..........%baking soda
6.35............50.00
6.5..............58.55
6.6..............64.01
6.7..............69.12
6.8..............73.81
6.9..............78.01
7.0..............81.71
7.1..............84.90
7.2..............87.62
7.35...........90.91
The Y axis is the percentage of baking soda that converts into carbon dioxide.
The X axis is the pH.
As you can see, most of the bicarbonate converts into carbon dioxide when the pH is below 6.35.
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