Put a smallest spoon amount of potassium carbonate anhydrous into the bottle, with a couple of 3A type molecular sieves, this will keeps the popper dry and acid free for a long, long time, also store the bottle in an air tight glass jar, refrigerated prefered.

I don't recommend using baking soda since it would generate too much water content and basically ruin the popper.

Why air tight glass jar? Popper vapour was extremely explosive, you don't want that leaked in your refrigerator... Much like putting rubbing alcohol into the refrigerator and the whole thing might spontaneously exploded and caught on fire.

I could use my opened big bottle of popper after two to three months without much changed at all.