Hi,
I have this camera myself so I may be able to help you a little bit.
First thing I need to know is what type of lense are you using to take the macro shots.
Is it the stock lense, 18-55mm, or the zoom lense of 75-300mm?
or do you have an actual macro lense like the 100mm f2.8 usm?
If you don't have the actual macro lense, then you will not be able to get completely up close to the corals as they will be too blurred, but you can still get some pretty good up close shots.
First thing to do, when first learning this camera is to use the pre-settings. If you are looking for close up shots, then put dial on on the flower selection.
White balance should be set to automatic.
When shooting your subject, especially through tank glass you will want to do this head on. If you need to, rest the lense against the tank glass to get as close as you can and to steady the camera if your hands are a little shakey.
If you attempt to shoot on an angle it will blurr the image.
If you need to, purchase a good solid tripod or one of those and get a remote so you can take the pic without touching the camera to reduce shake. (I need to get one of these for taking pics with my macro lense when on my tripod.)
Ensure that most of your powerheads and major water flow moving devices are off. This will help with quality as the corals won't be swaying when you are trying to take pics. Most people do this.
Buy a large sdhd card, 8gb or more. Any good photographer knows that it takes many pictures to find one good picture. It is not uncommon to take 30 or 40 pics of the same subject with only 1 or 2 being acceptable to show others.
When shooting fish, you will want to put it on the setting with the running man. This is the setting to take action shots. It is much harder to take images of fish than free standing corals. The main thing to remember in this instance is to have the eyes of the fish in focus if nothing else. This will create interest and a connection to the subject.
When you are ready to use the Manual part of the camera, it will take some time to determine what lighting and shooting perameters are needed. It may be different with each shot you attempt to take, or whether you are shooting in full lighting or actinic.
Remember, don't get too frustrated at first. Photography does not come easily to everyone. Trust me. I hated taking it in College when it was part of my journalism class and had to use a 35mm with film. Now I like it a lot better, but have to relearn everything.
There are some really good books on digital photography available on amazon.ca if you are interested. They may help you to learn your camera better and expand your interest in taking photos.
Also, for taking pictures of your reef tank, the following website, FICKLE WATERS has a great section here on Digital photography for reefs and has a little info on composition, dealing with blurry photos etc.
http://ficklewaters.com/category/photography/
If you have any other questions, please feel free to ask.
I hope I was able to help you a little.