It can be caused by internal parasites or vitamin deficiency usually. Vitamin C is often needed
Click the nutrition box for details
has ascorbic acid which is a form of vitamin C
You can check other foods in case you already have some kinds of food with ascorbic acid or vitamin C
Some of the treatments could damage biological bacteria and or snails /shrimp.
You can check on Seachem Paraguard or Prazipro
PraziPro - Hikari Sales USA