I am attempting to establish a qPCR standard curve for a SELEX starter library (randomized sequences) using SYBR Green, however anything above 1ng of DNA creates a curve that starts in the negative range and climbs to 0 RFU where it flat-lines. The reactions in this image 25uL with 5 (red line), 0.5, 0.05, 0.005, 0.0005, and 0.00005ng of library DNA. I've tested this multiple times and every time the amount of library goes over 1ng, the fluorescence starts at a negative RFU reading and goes to 0. Is there a way to adjust for this?

System: CFX96 Real Time System

Software: CFX Manager