Ich is a common parasite that shows as tiny white salt-like spots on a fish's body and fins, usually triggered by stress or a temperature drop; it is treatable if caught early.
Because the parasite has a life cycle partly off the fish, treatment (often raised temperature and/or medication over a set period) must continue long enough to catch the free-swimming stage. Follow a proper protocol rather than stopping when spots vanish.
This is general guidance, not a diagnosis or prescription — for a serious or unclear case, or before medicating sensitive fish, shrimp or scaleless species, consult a fish-savvy vet.