Snails Shell has turned white

[TheLegendaryBarlowe072]

Im wondering if anybody knows why this snail's shell has turned white? Otherwise it appears active and healthy.

 

[Timfish]

Have you checked if the white can be scrapped off with a finger nail? My first guess looking at that picture, because of the evenness of the appearance of the white with a little bit of the original shell color along the back edge of the foot, is an encrusting sponge. If it is a sponge it should scrape off easily with a fingernail, and I'd consider harmless for the snail and beneficial for your system.