See the dark spot/area on my night guard here?

Okay I will try that, with bleach & some water, or just bleach to try that with?
Or any other liquid stuff to use with bleach too?
Then I will make sure to rinse it off thoroughly before I will put it in my mouth(rinse it off with water for a while?)

Bleach and water. Rinse with water. Never mix bleach with any other chemical.

Why not?  How else am I supposed to make chloroform?

Okay, will do just that.

Maybe mix just half water & half bleach-whatever the amount of water & bleach I will mix with it?

Pretty sure a half bleach and half water would be way to strong and probably not healthy. Anyway I was thinking that maybe a Polident Denture Cleanser tablet would clean up that dark spot. Cheers!

I had tried Effordent, is it almost like Polident of what substance in it?
And that wouldn't get (any) dark stuff off of my night guard-probably don't know what any of other solution to make & try to see what other solution would work tor that-is it?

Well I tried the other stuff (& steps) & at a dentist place, then none of that can seem to get any of that off, then I went & post it here-

Actually it got all rinsed off, it's just dark stain on it.

One other posted thread I saw might be some gross too!

Yeah, I guess I may get a new one after the next dentist-even that the (plastic) night guard is really quite expensive!

I may try that other suggested solution first