When conceiving molecular communication (MC) systems, it is of utmost importance to determine the threshold value for decoding bits and producing the smaller bit error rate (BER). At this optimum, the BER has the smallest value, and errors in the reception can be minimized, thereby improving the minimal throughput of molecular means. Despite its importance, prior research still presents little applicability and insights obtaining the optimal threshold for real testbeds. Filling this gap, in this paper, we feature a low-complex algorithm for the optimal threshold in single-input single-output (SISO) testbeds. Using a self-adaptive method, we assess a threshold close to the optimal, whereas the BER results are close to the minimum achievable. Furthermore, we show that for real existing molecular communication systems, an optimum can also be determined with respect to the BER. The BER can thus be reduced by up to 90 %.