Thx for the comments!
About the violet water - my holy grail is absolute minimal colour grading in post, because grading slows editing and rendering. Unfortunately, on this trip I did something a bit stupid before a whole bunch of dives which was to experiment with setting the saturation in camera to +2. I guess I need to do some more colour grading after all.... If the grading works well, then I'll replace the video.
Davide - yep normal PZ 14-42, but it's behind Nauticam's WWL-compatible port (N85, GH5 variant). There is maybe 1mm at most between the front of the lens and the port. There are certainly better quality lenses, but it's small, cheap, versatile, and you can control the zoom electronically with a Fn button. The manta close-ups were at 42mm.