Ridiculously overpriced citric

As can be seen even in the product description of kalkreinigers, is the descaler to "100% citric acid" common citric acid. 5kg Pure citric acid, in crystalline form, of Purux, you get in a Marketplace dealer for about 23.85 incl. Shipping. Even if one now calculates the Melitta descaler without, and the Purux with shipping, so there is a difference in price by 6.5 times in favor of Purux citric, normalized to the kilo (Melitta 31, - / kg, Purux 6.50 / Kilo). And this for a chemically identical product.