Hi Tom,
I am not very advanced in photo skills but I will give my best to explain my point of view.
If anybody else has something to add, please, do so.
So, I am using Nikon D5200 DX (which is not full frame) camera and maximum focal length I've used for taking photos of the tank was 35mm DX lens.
For taking whole tank shot I warmly suggest to use as wide lenses as possible.
For my DSLR camera ideally would be something like Tokina 11-16 lens.
Using wide lens (11-18mm) promotes visual effect by providing more "depth" by elongating back sides of the tank.
Ones you have used (85mm, 135mm and 300mm ) are not suited for taking this kind of photos.
They are great to use outdoors and for macro purposes (85mm) but not very useful for our hobby.
Regarding light issue, if it is possible, you should use as much light as you can put on top of the tank including studio lights or extra LED (or use flash with wireless trigger).
It gives you so much more space for higher shutter speed and lower ISO to get that "crisp" effect.
That also goes for taking macros...more mm usually demands more light for taking nice photos , specially if you are going with the higher aperture (f7-8).
I hope that this was helpful...
Thanks Ivan for your advice. I have some quite wide lenses which I will certainly use for full tank shots as you suggest. In hindsight, reading my post, I wasn't clear - but my question is really about doing macro photography.
My camera is similar: not full frame, but micro four thirds. So if you are using 35mm full frame DSLR lenses with adaptors (as I do), you have to multiply the focal length by 1.5 (with a speed booster attached, without this you multiply by 2.2) to arrive at the actual magnification. So I'm assuming this is similar with your camera, and hence the extreme wide angle lenses you choose. I will experiment with wide angle to see the effect on the perceived depth that you describe, so thanks for that tip.
I've since done some reading on macro photography, and realised that there was a lot I didn't know about macro photography! Most of the photography I've done in the past is portrait and landscape, and so none of my lenses are macro lenses. The sorts of images I want to capture, apart from the full tank shots, are close-ups of natural fish behaviour. I love the details, patterns and surprises that macro photography reveals that you can't see with the naked eye. And I like the sort of nature shots that make you feel like you are "in the tank" rather than a neutral observer.
What I've discovered (I feel stupid saying this, as it shows my ignorance... but I didn't know what I didn't know!!) is that macro lenses are quite different from normal lenses (surprise surprise!) in that they are optimised for use at their closest focusing distance which is the opposite of a normal lens that is optimised for use at infinity (that's what the blog post said... Ken Rockwell I think it was, who I've relied on for lens and photo gear reviews and advice for years). And also I hadn't thought enough about subjects like depth of field at such close distances, and the effect of motion blurr; so my reading has revealed some of the reasons for the techical problems I'm having...
In short, I plan to use a flash to fix the light issue for macro. And I'm looking into a second hand macro lens - either approx 100mm or 200mm.
I will experiment as you advise with my studio lights. I have two 800W studio lights, so they are more than powerful enough to make the tank blinding... I'll have to use diffusion and maybe even bounce the light, I'll try and see. But I still will need flash for macro work to freeze the action and use higher shutter speeds...
Thanks again. I'll let you know how I get on. If I managed to produce any half decent shots, I'll post some...