OK, so I may be way off with this, please bear with me for a second. I like UW photography, and I prefer using natural light (just a personal preference - I'm a bit more of a landscape person (or sea floor scape in this case). I use Sony RX100, it's small yet functional enough for me under water. I'm however struggling with setting white balance - automatic WB is painfully bad and is a mess to try and fix in post-processing (shooting RAW of course). The only thing that worked for me was presetting WB off some target underwater. I have to do it every 5-10 ft of depth to keep it accurate but it beats having nearly unfixable blue/green tint.
My problem is that it's hard to find a more or less accurate target for WB preset when under water. When I can, I use my buddy's grey tank, but it's often a bit too far to be convenient - ideally it needs to be 1-2 ft away to be a reliable target. Sand patches don't really work either, they are off yellow or some other crazy tints. I even contemplated carrying 18% grey plastic cards but it becomes unmanageable since you now have to hold two things when presetting WB, and keep doing it every 10 minutes as your depth or lighting conditions change.
I think I came up with an idea to fix this problem. Before I continue though, is it just me living under a rock and the rest of the world solved this somehow? Is it even a problem worth solving for you all? Or do you just bring lights and preset your cameras at 5000 K or whatever your strobes / floodlights give you? Interested to hear any comments.