Is the background vinyl and/or waterproof? If so, spray water on the glass and squeegee the background on, makes a ton of difference rather than taping it.
If it's waterproof then I guess squeegeeing it on isn't an option.
A lot of those aquascape pictures with white backgrounds or light blue backgrounds that look like a sky, are usually lighting tricks (extra lighting is used)
Some DIY ideas on white backgrounds,
http://www.plantedtank.net/forums/120-aquascaping/351833-white-background.html
still extra lighting is used to achieve the more intense bright white.
The glass and water itself "color" the white background. So does the lighting itself (depending on bulb Kelvin).
I believe a glossy white background would be more reflective, appearing a brighter white in comparison to a matte/flat white.
If you just had to can't find a proper white vinyl background, I guess you could paint the glass white, not too hard to scrape off glass if you want to change later.