@kmnagy It is a very faint tint in the corners and seems like it could be a gelatinous film. It's hard to see, but once you do see it you'll know what it is immediately. It is a bio-film that is bacterial...I think....or like an algae maybe, but it shouldn't be there. I was none the worse for it even though I found it probably a few days after it had begun to establish itself.

I feel that daily rinsing and refilling will take care of the problem in most cases, but it couldn't hurt to run a vinegar or light bleach solution into the chamber and swish it around once a week or so. Maybe even peroxide would do it, which so many of us have in our bathroom cupboards.