Seafood soup usually tastes fresh and delicious, but if you want to increase the sweetness, you can consider adding the following ingredients:

1. Corn: The sweetness of corn can add sweetness to seafood soup and increase the consistency of soup.

2. Purple sweet potato: Purple sweet potato is a natural sweet food, which can help adjust the taste of soup and increase the sweetness.

3. Carrots: Carrots contain natural sugar, which can add taste and sweetness to the soup.

4. Onion: The sweetness of onion can increase the fragrance of seafood soup.

5. Jujube: Jujube is a natural sweet food, which can increase the sweetness and nourishing effect when added to soup.

It should be noted that the amount of these ingredients should be adjusted according to your own tastes and preferences to avoid adding too much sweetness and affecting the original flavor of the soup.