I am a hobbyist at plant tissue culture, I preparing my MS medium by formula (from chemicals) and I am getting a white film layer on the surface of medium after 7-8 days of incubation. I am not sure that it is contamination becuase it is not growing. Some times getting a brown/yellow film on top of medium. it is not growing also. Should I suspect my methods or my chemicals.. All my chemicals is %99 chem pure. Thanks for your help.