The manufacturer's data sheet says the unopened vial lasts for 2 years at -20 C and that the mix is stable at 4 C for at least six months. The dye we are using has been opened and has been kept at 4 C for a little more than a year. We are having trouble visualizing our PCR products on agarose gel when using this dye and our target DNA sequence is about 200 bp long.