Photography fits everyone on this site! An expensive hobby with lots of gadgets, most of which we stop using, and takes a while to get right.
Most of the shots I've posted were taken on a reef. Aquarium shots to me are much harder.
But imagine (especially if you've kept one) trying to get an image of a Royal Gramma. They never sit still, are always skittish,
live in caves or overhangs, and swim upside down. So they are moving, you are moving with every breath (scuba) and there is always some current.
The saving element is flash because it freezes action, and is necessary to see beyond blue/green color underwater.
The same can be true for the aquarium but for the issue of over exposing a reflective fish (true UW as well) and reflections off the tank surface. For the latter, if you have a DSLR one can be helped with this:
A new lens hood is gearing up for release that allows you to take reflection-free images through glass. Taking form as a silicone cone, the accessory, entitled Ultimate Lens Hood (ULH) can be stretched and adapted to fit lenses of varying sizes. The equipment is utilized by first attaching it to...
fstoppers.com
In the film days your number of shots on a dive was 32. You couldn't change film, and as above had no idea what you had until the film was developed, often days after returning from a shoot. With digital, UW is confined only by the lenght of the dive and there is instant feedback. Like on land a real game changer.
I don't recall ever getting a good film image of a Royal Gramma and it took hundreds of shots to get a few I liked. Post processing on this was minimal. The black background is a function of the flash and camera settings (and what's behind the fish). People who don't know marine fish can't believe the color is real.