One ounce bottle of Optiphen Plus.  Click to add multiples if  you wish more than one ounce.
 
Optiphen Plus is a patent pending globally approved preservative developed particularly for low pH systems. This liquid preservative system features an innovative blend of phenoxyethanol, sorbic acid, and caprylyl glycol. ... It may also be used selectively in formulations where the pH is greater than 6.0.