The bac water im going to buy is 30ml. im wondering it says it is good for 28 days quote ... "once a vial of Bacteriostatic Sterile water is open the preservatives will prolong its life for up to 28 days. After 28 days the vial needs to be discarded"... what im wondering is if the bac water will go bad or if just the mixed hcg will go bad and if so can i mix more with the same water. i dont want to buy a bunch of the water because its kind of expensive