The mildew on the underside of your cover is not out of the ordinary. You need to wipe it down every week or so after one of your post soak dichlor doses and you won't have that problem anymore. As far as the smell...I don't know. It could just be the smell of the O3 from your ozonator or maybe there's a lot of CC present. Do you test for CC? I know if I don't open the cover for a few days, I'll get a strong ozone smell.