The date of expiration must be written on the bottle at the time it is refilled.  Bottles of ultrasound gel must also have a discard date written on them when they are first opened. The discard date is 30 days from when the bottle was opened.  Unused gel in a bottle or a refillable bottle must be discarded at the end of 30 days or by the manufacturer’s expiration date, whichever comes first.