This is my first Island Mist Kit, Green Apple Riseling. My intial SG, after adding extra sugar, was 1.080. It fermented down to 0.985. I added the k-meta and sorbate. Degassed and added F-pack followed by Isinglass. The kit instructions say the SG after adding the F-pack should be 1.010-1.018. I checked the SG and it is 1.000 after the F-pack addition. I checked my hydrometer with tap water and it is reading correctly. What is the problem and why is it reading low?