The cleaner is supposed to indicate when cleaning is complete: color change from green to blue. My experience: The blue color stubbornly sticks to the limescale, which cannot be removed. You can't get rid of this blue color even with a lot of cleaning! Conclusion: this cleaner is useless! Instead of completely removing the limescale, it colors the residue blue! The limescale is marked blue for all to see! Not a clean toilet bowl, but the limescale is made "visible"! In this sense, the product has been given the right name...