Hi Maximumbob,
Cool xmas present! A couple of others got this model and have done some great work. Lighting is really a challengen with tanks because there is so much variation across the different areas. It's not clear what camera settings you used with the shots (ISO, metering mode,shutter speed, fstop etc), what file type (jpg vs raw) or whether there was any post shot processing (Photoshop etc). There are a lot of ways to skin the cat so a good thing to do is to have that "exif" data that comes with each shot. That way it's easier to understand what corrections to make during or after the shot.
In the first shot the highlights across the top seem to be totally blown out. If there is one bad thing about digital cameras it's that they don't handle overexposure very gracefully at all so sometimes it's necessary to compromise the shot settings to avoid this.
This shot is overexposed to the extent that you can actually see some details in the dark areas like at the bottom right where the thermometer(?) is. Since that area is of no interest it would have been better to adjust the exposure down by 1 stop so that the thermometer and tank trim would go all black while the top would also be darker and therefore less blown out.
So let's say you were in P ("program auto") mode and that the camera selected the following settings for the shot; ISO 400, f5.6 and 1/125 second. There are a few options you could use to lower the exposure but the easiest way is to use exposure compensation.
This is the button, looking at the top of the camera, just aft of and to the right of the ON/OFF lever. It's labeled "+/-" If you hold this button down and spin the rear dial you'll see in the viewfinder numbers with + or the -. "+" forces the camera to make the photo lighter than it would ordinarily and while "-" makes the shot darker than it would. If you rotate the dial so that "-1.0" shows the shot will be "1 f-stop" darker. That effectively means that the shot will be twice as dark as if you hadn't fiddled with the dial. "-2.0" would mean the shot would be 2 f-stops, or 4 times darker and so on.
You can just play with the compensation until you get an exposure that achieves the best compromise of well lit, medium lit and dimly lit areas across the frame.
After each shot you can review the image and zoom in to review each area of the frame. If you are outside and if it is difficult to see the display image you can use the histogram to tell you if you have significant over/underexposure. If you want to know more about using the histogram let me know.
Cheers,