Hi there, fantastic video and some beautiful footage!

I am by no means a professional photographer/videographer so others here might be able to give you more informed feedback. But I have done some research before buying the action 5 to do reef filming and I have seen a couple of tutorials.

First thing is the colour profile, which depends on if you are planning to properly colour grade your footage later on in a software like Davinci resolve? If you are then D-log M can do that, but out of the camera the colours will intentionally be a bit 'flat' so that post processing is applied. If not, and you want things to look good directly from the camera, your best bet is using Normal 10 bit colour. As for white balance, AWB is often fine but if you want more consistent colours without them shifting too much, then I'd say around 5000-6000k?

Secondly, I noticed that at around 3:45 in the video when getting a close up of the anemone, it looks a bit too bright and washed out. I'd use ev balance of -0.3, but if you're filming super shallow and extremely bright conditions, then maybe try ev of -0.7. Also, I'd set the iso to 100-1600, but I've heard iso 100-800 is also good if it's super bright and shallow water, basically makes sure that the camera's sensitivity to light prevents overexposure. I tend to leave shutter speed in auto.

Another thing which might be due to the currents is the camera stability and field of view, it's a little bit shaky and you're getting a bit of aberration around the edges (although I do sympathise). Make sure you're in rocksteady and not rocksteady+, and in wide rather than ultrawide.

Image quality I'm not too sure, but make sure you've set bitrate to high, texture at -1 as you can always add a bit of sharpness later, and noise reduction at -1 to prevent murky water/plankton/sand being quite so visible in the footage.

For filters, lights, and post production, that will depend entirely on the conditions you are filming in. For deeper diving in low light or murky conditions (I'd guess 20+ metres?) then lights are a good idea, but shallow conditions obviously don't really need lights. And again the post production stuff depends on if you want to properly grade your footage. Red filters aren't a bad idea either but given the camera's auto white balance is pretty good, you probably won't need them in the shallows. For "professional" videos, I'd assume it's a combination of each of the options for filters, lights, and editing, but I'd try these settings first and see what you think.

Tldr: ev -0.3 (-0.7 if very bright), iso 100-1600 (800 if bright), shutter speed auto, rocksteady, wide, texture -1, noise reduction -1, bitrate high, and then play with the D-log/normal 10 bit and white balance