Developer here, can you tell me which stars you've cleared? (blue star, yellow star or green star). For the rest they are actually all related. I've written down the hints below.
SPOILER BELOW:
1) How to get the fish out from the tank
- You will solve this one later
2) Where to use the fish scroll code
- tap/press the fishes (fish, whale, shark) in the order written on the scroll
3) Where to get the third star
- which color stars have you cleared?
4) How to open the container next to the shark
- you will open it once you've cleared the scroll code