Baking soda vs soda ash: Baking soda raises alkalinity without spiking pH, soda ash does both

Baking soda (pH ~8.3) is the steady option for boosting alkalinity in pools or aquariums without a major pH jump. Soda ash (sodium carbonate) is stronger and used when you want both alkalinity and a fast pH shift. Baking soda moves pH a little, not a lot—test after adding to be sure.