Reserve balance requirements series is the portion of the reserve requirements not satisfied by vault cash. The series is calulated as Required reserves (https://fred.stlouisfed.org/series/REQRESNS) less Vault cash used to satisfy required reserves (https://fred.stlouisfed.org/series/VAULT).
Board of Governors of the Federal Reserve System (US), Reserve Balances Required; Reserve Balance Requirements [RESBALREQ], retrieved from FRED, Federal Reserve Bank of St. Louis; https://fred.stlouisfed.org/series/RESBALREQ, April 22, 2019.
Total reserve balances maintained is the amount of balances institutions hold in accounts at Federal Reserve Banks that are available to satisfy reserve requirements. Historically, this series excluded balances held in a reserve account for contractual clearing purposes (contractual clearing balances program has been discontinued on July 12, 2012).
Effective February 2, 1984, reserve computation and maintenance periods have been changed from weekly to bi-weekly. Series with data prior to February 2, 1984 have different values reported from one week to the next. After February 2, 1984, the value repeats for 2 consecutive weeks.
Board of Governors of the Federal Reserve System (US), Total Reserve Balances Maintained with Federal Reserve Banks [RESBALNSW], retrieved from FRED, Federal Reserve Bank of St. Louis; https://fred.stlouisfed.org/series/RESBALNSW, April 22, 2019.