You can set a low balance notification threshold from your Atomic account. The notification will automatically send you an email (email as per your profile) whenever your balance has arrives at the specific threshold.
Navigation: Profile > Low Balance Notification
The default value for the Low Balance Notification is set at:-
1st Threshold - 50% of your credit limit
2nd Threshold - 75% of your credit limit
3rd Threshold - 85% of your credit limit
Low Balance Notification settings panel showing three thresholds set at 50%, 75%, and 85%