I'm going to break it down by what I feel is the priority and see if this helps.
#1 It's all about having good gear and great video lights. The better you light the subject the better the color and white balance will be. Take time to hide in the dark basement and play until you know all the settings.
I've used a GoPro for years but recently switched to the DJI OSMO Action 4. I love the large sensor and auto white balance with its own external sensor.
#2 LESS IS MORE!!!! Shoot short little 20-30 second videos. Nothing is worse than a long-winded video of the same fish or subject. It also makes it easier in post processing.
#3 Look ahead of you and think about the shot, as you approach the turtle watch for the best background and watch for head and eye movement. This will tell you what the turtles next movement will be. If he looks scared STOP. I like to swim away and circle back, then I just sit and watch before sneaking in for the shot.
And remember to get LOW!! Never video from above looking down on the subject. The best video or picture is one that looks correct from a normal point of view. And no one likes the fish bum videos!!
#4 Set your video light position prior to each shot and be ready. Never chase a subject.
#5 If you really want great video stay to one side of the group and SLOW DOWN!! Seriously if you think you're going slow.... SLOW DOWN SOME MORE!! I dive like watching paint dry.
Hope these tips help and if you think of anything else post them.
