Spicy World Citric Acid, 5-Pound (Food Grade, NON-GMO) for $13.89 at Amazon

Spicy World Citric Acid, 5-Pound (Food Grade, NON-GMO) for $13.89 at Amazon
This is very useful for cleaning many different things.
As soon as you receive it from Amazon, store it in a good sealing plastic container at room temperature, and it can last for years.
https://www.amazon.com/gp/aw/d/B000OZFECU