I designed these 18 mer primers to amplify a 700 or so bp fragment but they dont seem to work under any condidtions, I get multiple bands anywhere between 48-50 C. Their Tm's are 50 and 54 C. I have lowered the magnesium concentration to 1 mM and still got faint multiple bands. How can I get around this? I'd aprreciate any suggestions! Thanks! Rob