You need to measure the SG as you add the salt mix. Do you have a refractometer or at least a hydrometer? The salt mixes vary from type to type and even batch to batch from what I've seen so the directions may not yield the SG you are aiming for. I always add less than the minimum directions and bring it up gradually from there. It's easier for me to add salt than it is to add water. Top offs need to be made using RO.