 Top of the tank off the back of your toilet, if you see slime or growth in there, that's bacterial. That's bacterial iron, so that's something I fix, too. Rotten egg smell, you know, like I said, the hydrogen sulfide, and that's actually bacteria down there. So with that, I do UV light. I put in, like, an ultraviolet light along with carbon filtration. Oh, yeah, so it's something, like I said, something different every day.