We ordered two identical showerheads, none had the quality of the sales description. The water jet does not come specifically from the nozzles, but injected crisscross in all directions, and have done so for the first time. So it can not be due to calcification, which is to emphasize that the rubber pads are hard and inflexible that they could not so well cleaned anyway.
After a couple of weeks one of the shower heads is even "burst" downright. There was a short bang and since then the water comes from all sides out, however, practically no longer out of the nozzles. A shower is now completely impossible. So we can not use the shower heads.