it's not a white background, rather it's a studio lighting trick.
the tank has no background. they hang a white sheet around,
then light it from behind with 5000k or higher fluorescent lighting, so
you are looking through the back tank glass at a glowing white sheet.
then they photoshop out any wiring or plumbing left in the shot.
the wave effect on the top water line is done by simply using a fan.
the light and dark shadow on the rocks is from using halide lighting.
the black or white photo boarder beyond the edges of the tank glass
is also a photoshop wipe.
most prefer dark backgrounds in the back of their tanks.
if you search PTF you'll find lots of discussions on this.
I prefer a mirror behind my tank to increase it's depth,
but I also line the rear of my tank with stem plants so
the mirror does not distract my fish too much. one day
I hope to own a much a deeper tank with no mirror