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I use "pure citric acid" from Heitmann for the descaling of the kettle. 1 - 2 tablespoons of the powder are dissolved per liter of water and the solution boiled in a kettle. I leave the whole thing for 30 minutes. Then the lime is dissolved.
The solution then I then pour cold into the toilet, which is also nice and clean.
The citric acid is completely biodegradable and food clean - so it is on the package - and can be used throughout the household (dishwasher, washing machine, coffee maker, aquarium, tiles, etc.)
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