Nice looking tank, love the angel. I just noticed that it's a half round, this will compound the image quality as it's really hard to to photograph thru curved glass, tends to distort the image.
You'll have a sweet spot thats maybe 4-5" around where things maybe in focus, outside of that area you'll see the image quality start to fade.
I can't offer any advice on your camera settings as I'm not familiar with that particular model.