I've got the same camera. I agree that a book is the best way to start, but if you want some quick down and dirty advice to get started, you need to know three things that the manual and just playing with different settings can't solve for you.
1. Aquarium light is far bluer than normal white balance settings can handle. One way to solve this is to darken the room except for the aquarium lights. Make sure there are no reflections on the glass from windows or other light sources. Then tape a thin (normal) sheet of white printing paper to the front of the aquarium. Zoom in on it so that only the paper is showing in your frame. Take a photo of the paper. Then, before you take any other pics, follow your manuals instructions for setting a custom white balance (you go to custom settings and find white balance for this). Once you've established that paper on the aquarium photo as your custom white balance, use the custom white balance setting when photographing your aquarium. The only other way to get decent photos of the aquarium is to use a separate flash over the top of the aquarium while you are shooting.
2. For those crisp, beautiful close-up photos you often see on this forum, you need a decent macro lens. I bought a used canon 100 mm for around $300 for this purpose. Good lenses are expensive, but critical for great photos.
3. Use a tripod. It's very difficult to get "tack sharp" photos without one.
Once you have these things in place, you can begin experimenting with your settings. (Oh, I forgot one thing that I often forget when taking my own photos -- turn off the pumps so that you don't get blurry images of all the little things flying around your tank when the pumps are on.) OK -- now you can start playing.
For still images, you can set the camera to AV mode (second click down on the settings dial on the top right of the camera). When you press the shutter halfway down, you will see the settings in the viewfinder, and when you rotate the wheel next to your right index finger, you will see the first two numbers on the left changing. You are actually changing the second number, the aperture settings (how wide an opening the camera is using, which affects how much light is coming in -- the lower the aperture number you see in the viewfinder, the wider the door). The first number to the left will also change because in AV mode, when you change aperture, the camera automatically changes shutter speed for you to adjust for proper exposure (not too much light getting in and not too little). Try an aperture a few stops above the lowest setting on your lens (e.g., if your lens can go down to 2.8, try 5.6. Then try a few shots above and below this to see where your sharpest pics are.
For moving images, turn your settings dial one click to the left so that you can choose to adjust shutter speed by turning that wheel next to your right index finger. Set the shutter speed as high as you can without causing the aperture number to blink. If it does, you've gone to high for the camera to be able to get what it things is a good exposure. Then press the ISO arrow on the back of the camera and set the ISO to 800 or 1600. The higher this number, the less blur from moving objects (e.g., fish), but the grainier the picture will look. You can get rid of some of this grainy look (called noise) with a program like photo shop. Oh, and if you are using such a program, shoot your aquarium in RAW mode so that you can fix more problems if the photos need to be adjusted in photo shop.
Happy shooting!
. Wish you were my neighbor, haha, cause looks like im going to buy my first DSLR camera too. Thinking about getting Cannon 70D. Like the new focus technology, and the touch pad.
