I thought I would post about a great way to cover the back of your tank, since I have never seen anyone, on any board, talk about doing this. When I started my nano tanks, I was looking for a cheap way to cover the back, and since I like black, I also wanted it to be flat black, to minimize reflection.
I was at a craft store, when I saw sheets of the kids craft foam, about 2 mm thick. I bought 2 of them which I really needed only 1, but they are handy for other things as well. I cut it to fit the back of the nano, attached it at the corners with 3M double sided tape, and it stuck very well. Do not skimp on the tape though. Get the 3M. (Scotch tape like tape, not the foam 2 sided tape.)
Recently, I was wishing I could do the 40b the same way, so out of curiosity I googled 'craft foam roll', and wallah, up pops 'Darice craft foam roll'. 36X60-perfect for larger tanks. $10.50 on Amazon. I am getting ready to do my 100 gal, and it will be a PITA because the current back is put on with Vaseline. Uggh. And I am not moving the tank, so should be interesting.
But, if you don't want to go through painting, and other methods, this works well. I am not going to use the 2 sided tape at the top or the bottom, where the frame is, but instead use packing tape. If you apply the 2 sided tape just to the edge, and leave about 1/4 of it hanging off the corner of the tank, you can trim it with a box knife, or razor blade before you place the foam, and you can't even see it. Press the foam down well.
You can see what it looks like in my profile, on the 40b tank. It also comes in other colors too, if you like something other than black.
My Toys; 100 gal. Clown Loach tank, 40 breeder community tank, 7.5 gal Emerald Rasboras, & Dwarf Cories, 17 Gal. Aquascaped Rimless Cube, Pygmy Cories, Embers, Dwarf Cories, Amano Shrimp, 3 plant/shrimp tanks, 300 gallon formal water lily pond, 150 gal. pond.