In my gallery there are quite a few pictures taken on custom white balance. I have the same camera as you but unfortunately no external strobe. The thing with white balance is that it very easily gives you nice 0.4s times to hold your camera steady. At least one gets steady hands that way 
How do you set your custom white balance? I've used a piece of white writing board to do that. Seems to work quite well but you can still burn sand all too easily but as someone pointed out you can just underexpose the picture.
Happy diving!
How do you set your custom white balance? I've used a piece of white writing board to do that. Seems to work quite well but you can still burn sand all too easily but as someone pointed out you can just underexpose the picture. Happy diving!
