Excellent advice and guidance from Ricardo. Really breaks it down better than I ever have or could.
https://www.youtube.com/watch?v=Ag0dkFFZVWg
Not the greatest tutorial in the world, was basically flying by the seat of my pants on it but this is basically how I do things without going into as much detail as Ricardo has in this thread. Also this method may not be the right one with the beginner just starting out with no flash units or wireless remotes or any of those goodies. I will say that the bare bone basics boil down to a dark room, lots of light above the tank, and just knowing your fish. The fish are naturally curious being cichlids and most of our discus are EXCELLENT at begging for food....its a winning combo for photography because you shouldn't have to chase them around the tank to get some good shots. You see them every day, you know where they like to hang out in the tank, you know if Fish A swims by Fish B then Fish B will chase it away, just little routines you can pick up on to be ready to capture that perfect moment.
And I know it may not be for the beginners, but I ALWAYS use flash above the tanks for photos. This requires an external flash unit that most people don't want to spend money on, and its not always needed as indicated above, you can get good photos without it. I just like the dramatic light it gives. My goal is to make you, the viewer think its just tank light illuminating the fish but I will guarantee that it never is with my fish photos.
wild3 by
SCMatt, on Flickr
red3 by
SCMatt, on Flickr
Stendkertefe1 by
SCMatt, on Flickr
Test shots are a good point. Thank god for digital images now, fire away and delete what you don't want. I highly encourage to snap away, and don't be discouraged by only using a few pics out of hundreds. I'm sure Ricardo and Stan are the same as me, people on this forum have not or will not ever see 95-98% of my photos. They just don't make the final grade to post.