Snail shell question

[FinnedFriendBeginner]

I have a 1 month old tank and I added 2 mystery snails to it a week ago. Today, I see a thin layer of discoloration on both of their shells. I am not sure if it was there when I introduced it to the tank. Does know if it is a deficiency or new growth. (I have crushed coral in the tank since 2 weeks and ordered some Wondershell in case)

Ph 6.8,GH 120, KH 40

[Lennie]

That is a new growth in a different water parameter. Those lines usually refer to the times where they are moved to a new tank. 
 

therefore, for perfect looking shells, it is suggested to keep them in stable parameters. 
 

it poses no issues tho, just visually less appealing

[Huckleberry]

It could be nothing but pick the snail up and see if the new growth on the shell is super thin and fragile. If it is then I would recommend adding something to the tank. 

[Cinnebuns]

I agree with both comments so far. The one problem I do see is your ph is dangerous for any snail. Acidic water will eat away at their shells causing rot over time. This will cause their nice shells to become pitted. Hopefully that crushed coral will help raise your PH. Do it slowly. Don't rush it. Changing PH too quickly will kill the animals.  

I do agree that it's best to check if that new growth is thin. That is A LOT of growth for 1 week. When they grow quickly, their shell becomes thin. What temp are you keeping them at?  If the temp is too high then they grow too fast to keep their shells healthy. 

[FinnedFriendBeginner]

Thank you all for your help. 

@Cinnebuns Temperature is at 78. I tried touching the shell and they seemed to be the same thickness as of rest of the shell.

I did a water change yesterday and hoping the crushed coral would raise the Ph as you mentioned.