Monte had ways to balance detectors both with an all metal threshold mode and also one without all metal. A good GB cancels out minerals to increase depth.
If you have an all metal mode, adjust the threshold up while off the ground and turn it up so you can hear it. With your coil about 8 inches above the ground, lower it quickly. If the threshold gets louder, turn it down by going negative on the dial. If it gets quieter, turn it up. Adjust until the threshold doesn't change when lowering the coil to the ground. Some detectors can do it automatically by pumping up and down, some have a mode to automatically change the ground balance. A search on the internet for your detectors 's manual should tell you all you need to know.
Monte also used a method in discriminate mode to set ground balance. He would lower the ground balance until the detector sounded of when quickly raised from the soil, then slowly raise it until the moment it stopped sounding off. He then called it good.
Good luck and I hope you do well.