Right, so let me share a few tricks with you on how to set up a photo-tank. I learned this from some other fishkeepers, and have tweaked it to suit my own preferences
I use a rather small aquarium, 30-40 x 20-25 x 20-25 cm (12-16 x 8-10 x 8-10 ''). This makes it possible to furnish it nicely, but still keep the fish visible up front. I use a glass divider in the middle of the tank, in this case I simply used the cover glass that came with it. I removed the glass holders that the cover glass was resting on, to make access in the tank easier. Then I glued the cover glass to the sides of the tank with aquarium silicone. This divider is important, because it means I can furnish the tank on both sides of the divider, but the fish will still be up front (in focus), although in the pics it looks like it has a lot of available space further back in the tank. I clean the glass thoroughly, outside and inside, and check for scratches and marks every now and then.
In the back chamber I place a small filter, in such a way that it can't be seen in the pictures. This filter is important, because it keeps the water in the photo-tank crystal clear. I fill it with regular filter wool. I will sometimes move the filter to the front chamber and let it run there for a bit, if the fish stirs up some debris and so on. Debris is not welcome, because it really affects how the pictures look. With a macro lens, these particles will be very visible, and that's not very nice. Also, the added circulation in the front chamber will sometimes have a positive affect on the pose of the fish! I use tap water or water from an aquarium with very clear water.
I furnish the tank carefully. I need to think about how to avoid creating spaces inbetween rocks where the fish can "park" or hide. This has been the most challenging part of finding a way to create a good set up for pictures. I experiment a lot with different types of rock, wood, vegetation and gravel. Fine sand is not very useful, as the fish will stir it up and it will mean more debris in the tank. Recently I have avoided the use of sand entirely. As for the back chamber, I just try to make it look like a nice background, without making it very visible that there's a glass divider in there.
I use a natural looking background wall outside the photo-tank too, again to make the end result look more natural.
Lightning is very important. I don't use a flash, because I don't want the reflection of it. So, I need to have the right kind of lightning above the tank. I use various LED-bulbs and lamps, and I experiment. Sometimes I use more, sometimes I use less.
People ask me how I make the fish pose so nicely, and that's not always easy! Catfish are good models, they usually stand still for that very short moment needed to make a picture. But, I still need to be quick, and sometimes it's just hopeless. Some individuals will not stop cruising around in the tank, and that makes photographing them very hard. However, they usually pause at some point. Some fish are pretty calm, and can even be led to pose in certain angles with some trickery! I use a pipette or plastic strip to very gently poke them or shove them into place. This even aggritates some fish, making them flare and show their best colours! However it's not always that easy, trust me. Some just need to be left alone in the tank for some time first (15 min - 1 hour), before they settle down enough. Some fish will never give in, and make me give up. Also, a steady hand is good to have - or you might want to consider a tripod for the camera. I like to be able to move freely, but if I had too much coffee or lose concentration, the result will not be good. I always try to aim for the eye when choosing focus point with the camera.
A couple of shots of my recent set-up:
I was looking through my archives for a pic of my photo-tank set-up, but couldn't find it. I will make a new one tomorrow. Anyway, I'm by no means a pro at this, I just learned a few tricks along the way. Certainly, a good camera is helpful, but not absolutely necessary. A smartphone will actually take you a long way! However, a macro-lens is nice to have, to display details better. Currently I'm using an Olympus Pen e-pl7 camera with a M.Zuiko Digital ED 30mm F3.5 Macro lens. I will show how I do the tank set-up tomorrow, when I have new pictures of it 
The background is simply a commercially produced type, chosen because it looks fairly natural.
The H.lunaorum is actually not very green, it depends on the light! It looks black in normal lightning. But it does have both white and yellow dots, which is cool!