Tetras don't enjoy unfiltered light, and they're not the type of fish to stand their ground. A few decorations and a lot of plants block out the intrusive light and give the small swimmers a place to dart into in the event that another fish gives them a menacing look.
Tetras in general enjoy filtered light, which floating plants provide. Something like water lettuce will provide a nice mat of plant life at the top of your tank but still let through enough light to reach the plants at the bottom of your tank. Despite their preference for some shade, though, your little tetras are not trolls -- they do enjoy some light to filter through, so remove plants as they build up and blot out too much light. If your plants at the bottom of the tank are declining in health, it's probably because they're not receiving enough light. Floating plants have a tendency to turn black and rot fairly quickly, so pluck them out as they do.
With so many types of tetras, there's also some variety in their preferences. For example, bloodfin tetras enjoy broad-leaved plants, while glowlight tetras prefer fine-leaved plants. Adding certain types of broad-leaf anubias plants and a few narrow-leaf anacharis will satisfy both tastes. Regardless of what you plant, make sure your tank has plenty of vegetation to mimic a tetra's natural habitat.
While you would never call someone a tetra for being scared, these colorful fish are neither brave nor bold. They prefer plenty of hiding places to escape other fish in the aquarium, and to rest and relax. Plants provide a few hiding spots, but decorations make even better safe zones. They also spruce up your tank in the process. Decorations that provide shade in the form of caves, coves and castles will have your tetras swimming into the secure spots for fun as well as to escape what they think is their impending doom when another fish challenges them.
Although they love hiding spots and plant life, tetras also need a bit of open space to swim. Placing the taller plants in the back of the aquarium and adding only one or two larger decorations -- depending on your tank size -- will provide plenty of open water for the speedy schooling fish. If they're crammed in by plants and decorations, they won't be happy and can even become stressed.
A black substrate helps darken the tank, which caters to the tetra's natural habitat. It also brings to life your aquarium by contrasting well against the green plants and bringing out the bright colors of your tetras. The only downside is that all of your efforts to clean the tank will be for naught in about a day or two, as debris shows up easier in dark substrate.
- Dwarf Gourami & Neon Tetras image by Ronnie from Fotolia.com