I have 2 turbos in my 60g. I Have noticed that the front of there shells is yellow. It is not physical damage but chemical. I have low alkalinity any tips to raise naturally and will the shells ever go back to normal. this is what the front looks like.
I’m fairly certain that the growth of concern represents the shell accumulation that has happened during the recent period of growth in the aquarium environment that you provide. The discoloration looks more like algae than shell material. Your lower nutrient system allows the shell to grow without a significant amount of algae on top.
Lots more could be said about the situation but I have observed this with snails and clams that have been relocated. The fact that the snails are growing is a good sign imo.
I have noticed them like this in my 20g. It's been like this for a couple months now. Then I bought 2 more and the other turned the same super fast. Then I transferred them over 2 weeks ago and they have been moving and eating.