I am testing biofilm samples from the tongue for universal 16s rDNA using Sybr Green qPCR. The primer set worked well for two years, but all of a sudden we are not getting proper amplification, super high Cq values, and bad melt curves. Does anyone know why it doesn't work anymore? We have ordered new stocks and those don't work either. We tried to look into other universal primers but we aren't getting as good results as we did when the old primer set was working properly. Any advice or suggestions would be appreciated!