Henry, when you say you set the white balance by taking a picture of a white wall, I am assuming that was outside of the tank? In order to properly set the white balance, you need to go into the white balance settings of your camera (see user guide) and set the white balance by taking a picture of something inside of your tank. Sometimes this can be done by taking a picture of the sand but you will need to ensure that the entire frame is white only (nothing in background, no rock, coral, etc). They also sell white cards that you can use for this. This will tell the camera what the color white "should be" when taking pics inside of the tank. This should help to balance out the other colors as well so that you can take a more balanced photo. With SLR cameras, most will shoot in RAW and adjust the white balance in post processing (with Photoshop type program). With a point & shoot, you don't have that option. So properly setting the white balance is key to ensure your pics aren't too washed out (or have that "glowing" look to them).
I am not a professional photographer by any means. I have learned what I know from reading a lot of the stickies on this forum and asking a lot of questions. I recommend you read any thread on here that gparr has started. He is a professional photographer (as well as a fellow mod here at R2R) and takes some of the best reef photos I've ever seen. He may chime in here as well as I'm sure there are more technical terms for the items I mentioned above. Once you are able to get the white balance set properly, your overall reef shots should look much more realistic. I hope this helps a bit.
Try some of these tips and post what you come up with photo wise. To give you an idea, if I take 100 pics of my tank, I'm typically happy with just a few of them. The key is to get your settings in order, take lots of pics, and have fun doing it! : )