I bought an apple snail and the new part of its shell is growing in a lighter colour and also irregular. What could be the cause?
It is because they have stopped growing for some time (transport to the shop, lack of food, other water quality) and when the animal start growing again (thanks to your good care) it’s unable to make the same quality of shell as it was before. When you get young snails, hatched in your own tank, you’ll see that their shell gets the right colour and that they grow more smoothly. But keep in mind that some species are more vulnerable to get a less smooth shell especially when they get older.