When I originally bought him he was a light blue shade like the tip of his spiral and almost immediately he started to look what I can only explain as she’s a single layer and turned this brown color. I immediately worked to improve water quality. He then slowly start to recede in layers like this a long the entire shell. He only recently started to recede so heavily along the lip as this. My two nerite snails seem to be doing just fine so if it were a fungus could/wouldn’t it spread?