Fixed the problem. The manual tells you to up the manual EV if the reading is "under". Hope this actually works.
I'll post some photos when I find the USB cable (it's hiding!)
Did you try it (changing EV)?
The "under" happened during WB I think is because there is not enough reflected light from the white/gray card or whatever you used (it happens even if you are in shallow water). e.g. if the card is v. very close to the lens. I tried to move the card a bit further away from the camera then it worked (if the card is small and cannot cover enough, you can zoom in a bit). If I continued to move the board even further, it said "over".