12 to 22 gpg is a huge range. It converts to 11.5 - 21 dH and 205 - 376 ppm.
Is it possible to narrow it down?
Your pH, can you test both freshly run tap water and some that has been allowed to stand for 24 hours, please. You may well find they are different. With hard water it is not unknown for water suppliers to add something to lower the pH to prevent limescale deposits in the pipe work. This will gas out when the water is left to stand.
It is unusual to have such a low pH with hard water; you may find it goes up after standing. However, I do need to check - do you use a water softener? That would lower the pH of the water coming from the tap.