I have been using the Schaeffer diesel additives for quite some time. Virtually all the diesel I buy is 10-15% biodiesel. I go thru over 20,000 gallons of diesel a year. The Schaeffer additive is very good, and at the recommended application rates, is a very good value. In the last 3 diesels I have owned, I have racked up a cumulative 3 million miles on all of them and only had to replace one injector, and never have had a fuel pump or other fuel system component issue.
Now on the biocide thing, I dose the tanks every couple of months with FPPF Killem biocide. I have 100 gallon fuel tanks, and a couple of ounces in each side every 2-3 months keeps any diesel eating critters at bay.