Can I use baking soda to raise my pool's alkalinity?

Yes, and it’s cheap. Baking soda raises total alkalinity without spiking pH like soda ash does. If your alkalinity is below 80 ppm, use roughly 1.5 pounds per 10,000 gallons to raise it by 10 ppm. Dissolve it in a bucket of water first, pour around the deep end with the pump running, and test after six hours — overshooting makes pH hard to adjust.