Weird color in shell

[princessboo]

Hello fellow snail lovers.
I'm coming here again for help, as my snail is having some strange changes in his body.
He had a little crack on his shell, but he kept being okay and active. However, gradually, the color of his shell started to be very dark, unusually dark, never seen it on a snail like him.
So, today when I got home, I noticed that he is smelling bad, like fish or mollusc. I also read that this smell can be connected to dead snails or even sick snails.
He keeps being very active, he eats a lot, he reacts very well to any stimuli and didn't change anything on his behavior. Just the smell and weird coloring.
Can someone please help me with some information?
I feel like the worse snail mom ever.

Thank you in advance for reading.
 
Here is a gallery on imgur with pictures of Tammi, took just 10 minutes ago.

imgur.com/a/m6kBn

[princessboo]

Hi again.

Just for a quick update.
Tammi doesn't seem to move from the same spot for 4 or 5 hours. He is not responding to any stimuli now.
Tried to wake him up gently with a bath but he doesn't move. Also, the smell is worse right now. I don't know what to do, think or feel right now...
Thank you for reading.

[princessboo]

Hello once again.

I am super embarrassed (also relieved) to say that the fishy smell is not coming from Tammi but from the cuttlefish.
I seen some posts here about the smell from hell it gives.
Tammi is still having really weird coloring on the shell as you can see on the pictures and he is not very active. I managed to wake him up on the third try. I would still love to know if someone else had had a problem with this kind of dark coloring in the shell of snail.

Thank you for reading.

[flowersnail]

Hello princessboo,
I don't have any experience in this kind of problem but I think it is an infection. Have you checked into Tammi's breathing hole for clues? Maybe it's caused by parasites. I also suggest you to read on some heliciculture websites, where there may be more information... I know they're not the websites we snail keepers prefer but I think we'd better give it a try.
Good luck!