Mariss, I just went through this...my tongue was black and slimy for months. I tried scraping it off myself, no luck. I went to a regular cleaning and the dentist who changed my toothpaste to one for dry mouth, didn't do much helped a little. I drink tons of water per day anyway. Went to my internist she put me on swish and swallow Nyzoral anti fungal didn't help much the first time.
I changed from PG/vg mix to Virgin VG...within a week along with using the antifungal again the black is peeling off my tongue like chunks of brown stuff scraped off. I can see regular pink tongue in places again.
So I have to assume that I can't use pg/vg mix only vg. I mostly use coffee type flavors had a lot of trouble with menthol types when first
vaping but more allergy type symptoms. I have to assume to I have a sensitivity to some flavors too.
So good luck.