I stopped using Star San years ago and went to Saniclean since it does not foam like Star San does. I keep mine in a 5 gallon Gott cooler and use RO water to make the solution. I can get several months out of a batch of it before discarding it. As Denny said, if the pH is below 3 you will be fine.
Another thing I would do is to carefully inspect your kegs and beer storage vessels, including any fermenters that are made of stainless steel. If they have beer stone in them, that could serve as a place to harbor bacteria and other nasties. I passivate my kegs and fermenters occasionally to get rid of any beer stone. You can use an acid bath to do this or mix up Star San at a concentration of 1 oz. per gallon (recommended by SS Brewtech), fill the keg completely and let it sit for a few hours or up to a day or so if the beer stone is really heavy. This should dissolve it from the walls of the stainless steel. It will also work on glass carboys although I do not use them anymore because of the danger issue with glass. I get my acid concentrate from a dairy supply store that sells bulk milk handling equipment and it works really well on beer stone.