Mold (?) in private onsens at a ryokan??

I've been to Japan over 5 times now but due to tattoos I haven't been to any kind of onsen at all until yesterday. I'm staying at a ryokan with my partner and there's a private onsen included in the room, and the room seems to be, uh… covered in mold. I'm almost positive it's mold because of where it's located and the shape etc, there's no way it's mineral buildup as there is some of that too but I know that's normal and what it looks like.

There were also several very tiny bugs around the onsen itself on the wood which I assume to be some kind of mite but I'm not sure. My question is… Is this normal?? I googled it and was a bit baffled to see absolutely no one talking about this so I've now led myself to consider I'm a major outlier but I have a really hard time believing that. Unfortunately I can't include pictures in this post but I do have them.

When I arrived yesterday the mold was already there but the ventilation definitely was not on in the room. My partner found where the button was to turn it on and it is significantly easier to breathe in there today. Because I'm checking out in the morning I don't want to bother telling the staff but I'm also a bit nervous that they might see it and blame me for the mold/the room not being ventilated and then charge me. I don't know what to do.

I might be majorly overthinking this and this is a super common thing to be found in these private onsens but I seriously have no idea. Can anyone help a girl out?? Thank you! I will not name the establishment.

by iceebluephoenix