New accounts are not automatically added to a pool. You will need to manually add them.
From a pool
Navigate to Interest Pools in the left navbar
Select the pool to which you want to add accounts
Click on 'Add account' in the Bank Accounts section
Select a start date
Eligible accounts will be shown, which you can add to the pool
From bank accounts
Navigate to Bank Accounts in the left navbar
From here you can add accounts individually, or in bulk, to a pool
It may help to filter on unconfigured accounts - these are the ones for which you still need to assign a pool
Exclude from pooling
You can also choose to exclude an account from pooling.