Here is some more info on Ground Balancing in general Ground Balancing Your Metal Detector
On to actually ground balancing your metal detector! I am going to try to keep this as simple and easy to follow as possible. I am also going to let you know up front that ground balancing your metal detector improperly can produce negative results, yes lost depth instead of gained depth. Again don't get discouraged! Practice makes perfect.
Lets begin setting your metal detector up to be ground balanced. The first thing you will want to do is put your metal detector in all metal mode. This will probably be required by your metal detector to manually ground balance it.
You should now adjust your metal detectors threshold. A basic rule of thumb here is to keep it at an just audible setting. Turn it down until you can no longer hear it, then start bumping it up until you begin to hear the faint humming in the background.
You are now ready to start ground balancing your metal detector. To do the actual ground balancing you must find an area void of any metal items or structures, such as fences. Making sure there are no metal objects in the soil where you will be ground balancing is important. Remember the act of ground balancing is actually just discriminating out and ignoring minerals found in the ground. You do not want your metal detector to ignore anything but the minerals found in the ground that you will be metal detecting.
Its time to start the actual process of ground balancing your metal detector. Obviously you need to know where the adjustment is on your metal detector. Locate the adjustment knob, or menu on your metal detector. If you can not find it look in the manual that came with your machine. It should be labeled "ground balance" "ground compensation" "ground", or similar. The knob or menu itself will allow you to adjust positively and negatively. Once you have it located move on to the next step.
This is where a trained ear comes into play. Remember the threshold you adjusted just a few steps back? With complete attention on the steady background hum, (your threshold), hold the search coil of your metal detector above the ground by about 2 feet. Now lower your metal detectors search coil to the ground paying absolute attention to the sound of the threshold! What happened? Did the threshold go silent, or fade? Did it jump or get gain in intensity? If the threshold went dead, or faded you should now bump your metal detectors ground balance adjustment in the positive direction. If the opposite happens knock it down just a hair.
Repeat the above step until your metal detectors threshold remains steady when going from air to ground. You will eventually form your movements, speed and style for this process though the basics should always remain the same!
There you have it, you now know how to manually ground balance your metal detector. Practice until you become a master of manual ground balance and I will assure you that you will start to notice yourself finding deeper and more valuable targets.