fermented soda making, ginger-bug & sugar, vs. baking soda & citric acid

So I did a little test earlier, with my 750 mL carbonating bottles. I pretty much have the formula down for carbonating any sugary syrup with a ginger bug, but I have a friend that can't handle sugar very well, and I was told that using baking soda & citric acid, instead of ginger-bug & syrup, can carbonate sugar-free drinks for them.

Since I'm still making sodas for myself for now, I tried with some peach syrup in hot water, 500 mL into the carbonating bottle, 1 tsp of baking soda, dissolved, then quickly added 1 tsp citric acid, put the lid on, swirl to dissolve, and put the bottle in the fridge.

Couple hours later, I pop the bottle open, get a nice loud pop sound but I don't think any fizz. The drink is nearly flat. Is there an established amount of each for this kinda thing to let the proper amount of pressure develop, or do I just keep experimenting?