If you are getting blurry pics with the lights out, Try this, get as much light as possible from windows (shoot when it is bright outside) or whatever, try and position your self close to the tank at an angle to the glass never shoot straight on to the glass. look where you are standing if you can see the light source reflecting (like the window, or light bulb in the room) try and move up or down or stand where you can't see the glare and shoot from there. Depending on how bright you can get the room you probably won't need the flash. PRACTICE, PRACTICE, PRACTICE! Also try different lighting (window open with no other light or the other way around).