Tank backgrounds. Right at the start is the moment for you boldly to decide that you'll paint the rear wall of the tank. Once you've begun, it's too late to take this wise step. Don't get all set up and then realize that the view of the hanging filter box and the stucco-textured wall behind it, with all those electrical cords, offers a less-than-ideal setting for your fishes.
Let me urge you to paint the outside of your tank black. The plain dark background is undistracting, and it gives a sense of deep space. A black background isolates the plants and driftwood you set in front of it, and makes you think of the tank's contents as a composition. If black seems too severe for you, add a few drops of red paint colorant to warm the black to a midnight brown, or a dollop of green colorant to render a midnight green.
White is also a possibility, if that will make the volume of the aquarium blend more harmoniously with the wall behind it. Takashi Amano uses white very skillfully. Remember, though, that on a white background every speck of algae on the rear pane will show up to reproach your imperfect housekeeping.
Going for black, Matt Staroscik sprayed three coats of high-temperature ceramic paint for auto engine blocks he got at an auto parts shop. He masked off first with newspaper and carefully covered the top to prevent overspray. In his description he recommends you set the tank upright, to get the spraycan at the right angle. Matt used three coats, dried for fifteen minutes between applications.
Or sponge on a mottled effect of shadows. Werner posted at Aquaria Central, 29 May 2001, "I sponge-painted the back of my tank with several shades of green and some metallic bronze. It blends in well behind my plants and the variation between the light and dark colors adds depth. Remember to paint in reverse; the first paint to go on the glass is what you'll end up seeing. Use a natural sea sponge or pick bits out of a kitchen sponge to get a lot of texture. Get the sponge wet and wring it out well. Put your paint on a disposible plate, ice cream bucket lid, etc. Just squeeze the paint out randomly in swirls or blotches. Dab up the paint with the sponge and lightly apply to the glass; a slight twisting of the wrist will blend it a bit. Make sure to move the sponge around so you don't get a repeating pattern. When the paint starts getting mixed into all one color on the glass, it's time to pick up more from the plate. Let it dry before going back to fill in the gaps; the sponge will often lift half-dry paint. Choose a variety of light and dark colors of paint, since they will get mixed together slightly and lose some of their contrast."
That sounds good to me. The paint I use is acrylic latex. It washes up with water, yet it's highly water-resistant once it has cured. A drawback: it's prone to scratching (the h.o.t. filter's feet are the usual offenders), because it's little more than a film of plastic. On the brighter side, scratches are quickly repaired, even with a dab of paint on a Q-tip, and the paint comes right off with a single-edge razor blade, if you're reusing a leaky tank as a planted terrarium.
Prep the glass with rubbing alcohol to minimize paint-crawl. You'll need about three thin coats anyway, to avoid light spill through the streaks. Consider using an expendable mini-roller like the one in the illustration, which you wrap in plastic film between coats.
Though I think nothing gives a better impression of serene deep space than shadowless blackness, there are alternatives to a painted rear glass. I don't mean cheesy laminated photographs of classical ruins on plastic placemats filched from the Greek diner and stuck to the rear glass with mineral oil. (You thought maybe I didn't know!)
Just as nothing behind the tank should distract from it, nothing in the backdrop should compete with the complete world you create inside the aquarium. Don't waste time building dry dioramas in shadowboxes to go behind the tank. Concentrate your design energy on what you build inside the tank. For years I used metallic green backing papers with a crystalline or leafy texture. I admit I even did a trick with an angled mirror once. I guess we all do that mirror thing, eventually. In the end, like all New Yorkers, I came around to Takashi Amano black...
Sometimes even the most preposterous plastic background printed on an endless roll has a reverse side that is plain blue, shading from light to dark. That's the only side to use! Since you're creating an underwater landscape, the lightest shading goes towards the top, eh, unlike a terrestrial scene, where the sky overhead is darkest at the zenith. (Of course you wouldn't have overlooked this, but you'd be surprised...) A few drops of mineral oil spread over the entire outside of the glass pane first will make the backdrop adhere; after you've laid it down, use a credit card to eliminate any bubbles under it, smoothing from the center to the edges.
For fake rocks scope the "Rocks" page and links. Some excellent rocky tank backgrounds are permanently fixed in place. You have to decide on them now, of course, before the tank is filled. You might consider corkbark. If you can obtain large sections of natural corkbark, you can piece them together and silicone them to the rear wall, giving you a natural texture. (After many months, corkbark will lose some of its maddening buoyancy.) The back glass still has to be painted. The point of corkbark is that it can be planted— especially with small plants, like Dwarf Anubias or the gracile form of Java Fern. Use the plants to mask the edges of the pieces of bark.
Frode Roe has some excellent planted corkbark backgrounds among the aquascapes illustrated at his website. Frode also takes thick styrofoam sheeting and whittles it into rocky shapes with a knife and finger pressure, then paints it with stone-colored epoxy paint and silicones it permanently to the tank walls. Silicone, epoxy and styrofoam are all chemically inert, by the way. Seeing Frode's results was making me think that you could sieve fine sand over the wet epoxy paint for a grittier and more matte surface, and then voila! I saw Nicolas Provini's article on his décor artificiel made of polystyrène expansé with a finish that's poudré de sable ...see how easy it is to get the gist? ...and plenty of étape-par-étape photos to help you when your French fails, oui? You could easily pin Java Fern plantlets to your styrofoam rockwork, using a staple made from a short u-shaped length of wire or with a sewing pin or two.
Planted netting. Nancy Sweeney has suggested another kind of tank background, made of plastic netting planted densely with the small-leaf form of Java Fern or simply with Java Moss. Anubias barteri nana might thrive like this, it occurs to me: I save every smidgen of rhizome with a couple of leaves on it, and toss it into the plant nursery. The foundation is cut from a single piece of that moderately stiff plastic "craft" netting you can find at your local Hobby Hovel. A dark-colored netting would be less visible. The upper edge of the netting sheet gets lashed to a stiff plastic rod, using monofilament. Java fern plantlets and small hanks of Java moss get "basted" to the netting. To install the backing, the rod will be clipped to the frame of the tank. Since the whole assembly can be removed from the tank for pruning and clipping from time to time, or kept wet a week in the dark closet to eliminate persistent algae, it ought to improve with maturity. As Java Ferns outgrow their situation, keep replacing them. Fry would find safe refuge behind the netting; keep that use in mind when you're judging how "open" you want the mesh to be. The planted netting could even be added to an up-and-running aquarium as an afterthought. And it could be switched from tank to tank, too. Especially if it were full of rainbowfish or killi eggs...