Can I use baked baking soda for the water bath?
You can, but I'll leave it to you to do the weight conversions for the baking soda to water ratio. While some pretzel recipes recommend using baked baking soda for a more intense pretzel flavor, the baking soda loses some weight when baked, and I think it's just easier to scoop plain baking soda out of the container and into the water so that's what I'm doing here. You'll need 90 grams of baked baking soda, so you'll need to start with more than that to account for the loss in weight during baking.