We recommend that you add a biocide to your testing solution to reduce bioburden and extend the life of your system. Possible biocides include Cosmocil QC (or the generic brand, Biguanide 20) or Proclin. ViVitro uses Cosmocil at a concentration of one drop per litre of fluid. Please use supplier concentration recommendations if you choose to use Proclin or other solutions. See wetted materials list in the specific user manual for material compatibility.