Your camera is good, but I don't know about your lens. For good pictures you can know any things.
1. Take pictures in RAW format.
2. Put the camera on tripid.
3. Don't use flash light.
3. Do maximum F number for maximum dept (better if it will be more 20).
4. Take a picture when camera stay parallel of tank glas. Better if camera lens will be close with the tank glas.
5. In menu switch of all noise reduction, sharpening and other tools. This is you can do it later in Capture NX, Aperture or other RAW converters.
6. In RAW converters do white balance on the white sand.
And last, the camera here don't important, the lens more important in photography.