Mystery Snail shell green?

Hello again... 3rd time posting this week as my tank has suddenly had issues for the 1st time. I had 2 deaths which caused a massive ammonia spike and my N02 and N03 are now also high which I am currently treating with new bacteria and more water changes, I have noticed my Mystery snail Gary, his shell has now got a green colouring and I just wanted to know if anyone could please tell me what it is? He has been put into a new tank today but have noticed this yesterday.

It looks like algae to me. It shouldn't be harmful to him, but a more experience member may chime in with more information. c:

Oh cool that what I had been thinking it was but then with all the issues with my tank currently I wanted to just double check with people more experienced

There is a bit of shell erosion visable, What are you feeding it?

Do you have soft or hard water?

My PH is 8.0 which is normal for Nelson water, hes just been moved from my tank that is having problems because I noticed his shell looking like it had some erosion. He already seems happier I was just slightly concerned of the green part being a fungus

The shell should not erode in water with a ph higher than 7. Erosion typically occurs in soft water with a PH less than 7. Any shell erosion that has occurred will not heal. The shell is basically rock. It is not living tissue and cannot regrow. Much like your finger nails. Food will only affect the new shell material created as the snail grows.

He had a small amount of erosion when I got him but I've had him for maybe 2 months now and I noticed it slightly worse so that's when I decided to move him and I've already noticed how much better he is doing so I guessed that maybe he was slightly stressed which caused the erosion to occur suddenly? This was him yesterday maybe an hour after putting him into the new tank