Cloud Aquarium will be unlocked once you complete the "Welcome a New Friend" mission. Its core function is to let you collect Pearls produced by the fish, then spend those Pearls to upgrade your aquarium and fish. There are several methods to earn more pearls, listed below:

1. Decorative Sand
In the beginning the bottom of the aquarium tank can only hold a maximum of 10 Pearls. Upgrade it to increase the Pearl storage limit. Once the tank hits full capacity, you must claim all the Pearls you have stored before your fish can produce more.

2. Pearl Fountain
You can buy the Pearl Fountain for Pearls from inside the Cloud Aquarium. The fountain automatically generates Pearls at set intervals. Level it up to increase its hourly Pearl output. When the fountain reaches its storage limit, you will need to collect all available Pearls to start its next production cycle.

3. Jellyfish Queen
You can buy the Jellyfish Queen for Pearls from inside the Cloud Aquarium. It boosts the Pearl production rate of all fish in your Cloud Aquarium.

4. Fish Upgrades
Level up the fish in the aquarium to get more Creativity Catalyst points and raise the Pearl output of your fish. All Cloud Aquarium fish can be caught via the Fishing Zeppelin.

5. Hermit Crab
At Cloud Aquarium level 5 the Hermit Crab will be available to purchase for Pearls. It automatically gathers Pearls and stores them inside its little coral reef home. Upgrading the Crab's home lets the Crab collect more Pearls. Once the Hermit Crab's home is full, newly produced Pearls will fall to the bottom of the aquarium instead. If the tank bottom also hits maximum capacity, all fish will stop producing Pearls until you collect them.

6. RC Exchange
You can exchange RC for Pearls directly.

7. Aquarium Pass
It's a permanent pass that unlocks at Cloud Aquarium level 2. Complete the following pass tasks to earn generous rewards:
1. Open the Cloud Aquarium once per day to earn 1 Starfish.
2. Collect Pearls once per day to earn 1 Starfish.
3. Upgrade the Cloud Aquarium by 1 level to earn 170 Starfish.
4. Upgrade an aquarium item by 1 level to earn 2 Starfish.
5. Upgrade a fish by 1 level to earn 5 Starfish.