4. Reduce heat to medium-low and add the coconut milk or Carnation milk (if using). Now taste-test the soup, looking for a balance of salty, sour, and spicy. If not salty or flavorful enough, add 1 Tbsp. more fish sauce OR soy sauce. If too sour, add more sugar. If too spicy (Tom Yum is meant to be spicy!), add a little coconut or Carnation milk. If too salty, add another squeeze of lime juice.