Jun, I tried your technique while I was in Bali waters last week, and I am not at all ready to publish the results! The reason is that the AF function (I presume) seems to add in blurring if there's a change in the distance to the subject. I didn't like the effect. I see that in your clips this happens rarely. Do you have a trick for preventing it?
Hi Marcia, aside from white balance/ going to C, have to also set focus to Manual (not AFS) to stop focus hunting, but too much work,
also discovered an easier way and how to save in WB custom mode (eg shooting molas)
1. go to underwater mode wide, can set white balance, preset prior diving at deepest depth where white balance can be done by camera
2. save settings - I just learned this on my latest trip and found this link how to save
It is confusing.: Olympus Talk Forum: Digital Photography Review
so at arnd 31ft or deeper, I just flick to C and no more adjusting, just saves me time if settings saved already, (for anything above 30 ft, use iA mode prior pressing video) wont be perfect color on shallower or deeper parts but we cant adjust WB all the time on a dive
on chasing focus, I still get clips which are blurred, reason why I cut the clips which are affected by hunting (rarely do I put in a clip longer than 8 seconds) if i'm not able to change from AFS to Manual focus mode, which happens almost all the time
most nudi shots dont blur since I keep cam at a stable position, slightest movement, it still chases focus on AFS

but after a while, especially with saving wb correction, can get used to it. took me 4 months and several dives to find out but getting comfortable with the steps now

lumix and canons dont require this much effort on video, has better afs iq