the balance tank - I would say is KAT - liquid storage and handling - below is from the guidance.
Handling, metering, surge, or other types of intermediate processing tanks used to control flow rates of liquid ingredients or product through the production system. Handling tanks also include tanks or totes where the tamper-evident seals are opened, and the container itself is used as a handling tank (e.g., when a drum is opened and a pump is attached directly onto the drum to meter an ingredient into the product line).
Are your vitamins locked / secured? Without knowing your system it think that could be your mitigation strategy (stored in lock / sealed cabinet and rest of system is "closed"
Good luck with the balance tank, back in the day i was lucky if they kept the lid on . Operationally, that one seems dfficult.
https://www.fda.gov/...113684/download