Questions about Riva Shower filter rivaALVA Skin&Hair EM - metal housing with filter cartridge

Are the replacement filters also available to buy individually? Or only as a set with metal housing?

How often do the filter cartridges need to be replaced?

Hello, I have two questions: 1) I have extremely sensitive skin. After a shower, my skin itches a lot and I've noticed that it's probably due to limescale. In fact, adding salt to the building's filter greatly reduces itching, but that doesn't make showers completely pleasant. I understand that this type of filter doesn't reduce limescale, but do you think it can help me enjoy the showers by reducing the itching too? 2) In view of the unavailability of EM filters on Galaxus. Are filters without "EM" compatible with this product? https://www.galaxus.ch/fr/s7/product/riva-alva-skinhair-1-x-filtre-a-eau-14356240 Thank you in advance!