1. Adjust water quality: Apple snails need high-quality water quality to stay healthy. If the water quality is poor, you can use filters or change water regularly to improve the water quality.
2. Calcium supplement: Apple snails need enough calcium to build a solid shell. Limestone, shell powder or other calcium-containing substances can be added to provide enough calcium.
3. Place small stones or sand: Apple snails can absorb calcium from small stones or sand, which helps them build strong shells.
4. Change the water frequently: Changing the water frequently helps to keep the water fresh and prevent the shell from turning white and cracking.
If the above methods can't solve the problem, it is recommended to consult a professional aquarium personnel or fish doctor.