Yes, you are absolutely correct, cr500_af. Every tank is different and may have different parameters based on many variables. These variables can be from the things you mentioned, along with source water, mixing method, surrounding environment, etc. There are no 2 tanks alike, I can assure you. You may have the exact same setup as your neighbor and use the exact same methods for mixing salt, however, the outcome is different. This is really inevitable in most cases. There are simply too many factors involved.