I've seen a lot (most of them) do not have a background on your nano tanks at all. im just curious if anyone actually puts a background or paints the back of their nano tank.
I have a beautiful GLA 6g rimless that I am setting up, however it'll be showcased in my kitchen area (don't worry, not near any appliances or anything like that).. but the wall color in my kitchen is a very light shade of green. i'm afraid the background of my tank will look like algae color lol
All of my "black" backgrounds are done with static cling window tint - the kind you can get for about $12 a roll at walmart. It's 5% light transmission so you could see through it on a window, but up against a wall it's pretty much black.
I don't paint mine, but sometimes I put construction paper up as temporary backgrounds when I need a change. I also do printed backgrounds, like a bamboo forest background on a betta tank. They don't last forever, but as long as no one inspects the back of the tank, they look decent.