Most of us who get a diffuser do it for the right reasons. We want a fresher home. to feel good about what we are breathing in.
But what nobody mentions is what happens inside the tank.
Your diffuser likely holds water, a reservoir of warm, standing water, run daily, refilled, run again. That environment is one of the most common places for unwanted microbial build-up in a home. Not because you're doing anything wrong, because that's what warm, standing water does.
The pink or orange ring some people notice is just the visible sign. Most of the time the naked eye can't see what's truly there, which is the part worth paying attention to.