Setting custom white balance on Canon G7X II and G9X II
Firstly you need to take a picture of something neutral, your hand, a white card or neutral coloured rock, sand, white coral.
Next, press the menu button
Choose Custom WB, press set.
Choose the picture you just took.
A prompt will tell you to Use WB data from this image for Custom WB, select OK and press set.
Move to the White balance menu, choose custom from this menu, its next to the K symbol, press set.
You now are in the custom white balance for the light conditions you are currently using.
Remember when lighting conditions change you will need to repeat the process.
Finally enjoy taking pictures of your underwater environment.