I 3d printed a PLA spool (cave line pocket reel) in two parts and crazy glued the parts together. That was 2017 August.
It's been in my pocket on every dive since I made it and is still in perfect condition. I dive every Sunday, dives lasting 70-90 min. It gets rinsed with the rest of my gear and then stored just like my delrin spools. No issues at all - not with the PLA, not with the glue.
I've also 3d printed a go-pro mounts and have been using them without issues. I 3d printed a ball mount for my SOLA 1200 - again no issues. All done with PLA. This stuff: AMZ3D 1.75mm PLA 3D Printer Filament, Black, 1 Kg spool (2.2 lbs) from Amazon. It's nice filament and has given no 'tangling' issues either.
I don't have Inon2000, but looking at your initial photos, it really looks to me like you are too far away. In some, the subject has some light, but the backgrounds, which are farther away, are showing no strobe light (just ambient).
You also say that macro is fine.
So my conclusion is the power from the strobe simply doesn't go as far as you would hope on those longer shots and so isn't lighting the scene.
You could try the strobe on manual full power in a similar shot and see if it lights the scene completely, but I'm betting it won't. However, that will be the tell. If manual full power DOES light the whole scene, then you need to play with either the TTL settings or some other strobe setting until you are happy. If full power manual does NOT light the whole scene, then you either need multiple slave flashes or a bigger strobe. In the latter case somehow you need to get more light than the strobe alone can give.
Interesting journey. Mine is similar... I've been using a G16 with a DS51 (wired TTL) + Sola 1200 video/focus light for years and love it. Last year I also scored a great deal on a Canon 7D and Nauticam housing. Mine came with 2x Ikelite DS125 strobes and the biggest focus light I've ever seen (old BigBlue).
I love the new 7D in the wonderful housing, but with the two strobes it was quite a monster. Just before Christmas I bought the Kraken (Weefine) 3000 Ring Light. I tried using it as my only strobe/light. It makes the whole rig very small and "clean" (for a DLSR in an aluminum housing!), but I wasn't as thrilled with the strobe as I hoped.
So I bought a used Inon Z240 which does TTL with optical and now use the Kraken as a fantastic macro focus light, with the Z240 for fill. It's great - almost as nice as my G16 (Ikelite housing) in TTL mode.
I use a 60mm lens exclusively simply because our vis off Vancouver Island Canada is never really good enough to justify buying a wide angle lens and dome.
I've looked at the mirrorless cameras, but am not super impressed - although the housings are definitely smaller. Ever since the root kit fiasco I refuse to go near Sony, but I am really liking the Fuji mirrorless cameras. If someone makes an inexpensive housing for one of the XT series that would be great.
Realistically, the Ikelite is a very good housing, but it's really on the low end of price. Try looking at Sea&Sea, Aquatica and Nauticam to name three and you will have white hair!
Also realistically, you will end up spending much more on strobes, arms and other doodads (focus lights, cords, this and that...) over time, so getting a good housing to start is actually a good investment. And ports! My god, the ports can be horribly expensive! With a good housing at least the ports will convert over to other cameras if you do upgrade down the road.
If you buy a cheap housing, you may well come to regret it.
The 6D is an excellent full-frame camera, so you should be able to use it diving for many years. Resist the urge (I say) to upgrade your camera every time the makers announce a new model.
You may also be able to get a great deal on a used housing for the 6D now that the mark 2 has come out. Canon moves the buttons just enough that older housings don't always work with the new model, and there's lots of folks wanting to upgrade.
I got my Nauticam housing AND the Canon 7D for a great price simply because everyone was selling them in order to get the housing for the new 7D Mk II.
So I'd recommend looking for a used housing (Ikelite, Nauticam, Aquatica, etc.) or if you are impatient just buy a new Ikelite. It's not that much.
Yep, that looks a lot like a classic "dead pixel". I usually see this on LCD monitors. The photo you showed - was this a screen capture, or an image from photoshop?
If it's really on the image, then it would certainly suggest a dead pixel on the image sensor. Does your camera have a "dead pixel" mapping function? I've never had to use the function on my cameras, but that would be the most appropriate way to address the issue if your camera has that capability.
Otherwise it would require post-processing. For photos - that's pretty easy. But I'm out of my depth on post-processing video. There may be some intelligent post-processing algorithm in the better video editing suites that would track that spot and remove it, especially given a dead pixel will not move at all during the entire clip.
The great thing about my housing is that it's really easy (even in big blue gloves) to invoke the menu and change the custom button functions underwater. So if this is really annoying me again underwater, I can disable that button 'on the spot'. Cudos to Canon for making that change pretty easy, and for Nauticam for making all the buttons pretty easy to use.
I'm noticing that there's just enough clearance in the camera mount to allow the camera to 'not be straight' in the housing when mounted, which may have been the cause of the errant AF-ON button pushing. I noticed the front dial was not fully engaged with it's gear, and closer inspection revealed the 'slop' in the mount when you tighten it up with a coin. If you don't ensure it's perfectly aligned when tightening the mount screw, the camera doesn't sit aligned in the housing. The only way this affects things is the front dial gear doesn't fully engage the dial, and the AF-ON button gets pushed a lot.
Tomorrow's the test of whether my alignment care pays off, or if I disable that button.