Furnishing

Labyrinth fish are generally fond of shallow water with floating plants where they can build a nest.

Fighting fish appreciate floating plants like this duckweed.
Image from Wikimedia Commons

They prefer a low water level. 15 cm is ideal if you want the fish to procreate, but they manage fine in deeper aquariums too.

Fighting fish like vegetation. They prefer to have floating plants or other plants breaking the surface.

Light

Fighting fish don't need a lit aquarium, but light is an advantage in order to see the fish, and to keep the plants alive. Rather than turning the light on and off at random time, you should use a timer. The fishes become less stressed when they have a set rhythm, the plants grow better, and algae get less of an advantage. It is best to limit the light period to twelve hours a day or less.

Heat

Artificial heating of the aquarium is necessary if the tank is not in a room with a stable, high temperature. The easies way to heat the water, is with a thermostat controlled aquarium heater. The ideal temperature for fighting fish is between 25 and 28 degrees Celsius.

Thermometer

When heating the water, it is also natural to measure the temperature. Aquarium thermometers are normally cheap. You can also use an electronic house thermometer with a sensor on a cord. Just see to that no glue or double sided tape remains on that which is to be lowered into the water.

Many electronic thermometers have a function to keep track of maximum and minimum temperature. One of these may come in handy if you suspect the temperature is unstable. The thermometer/sensor should not be placed too close to the heater, preferably in the opposite end of the tank.

An external aquarium filter.
Image from Wikimedia Commons

Filter

A pump driven filter is a good idea, also in fighting fish-only fishtanks. Without one of these, you will have to perform water changes very often. The bigger the fish tank, the bigger the filter. The capacity is most often printed on the box, in litres per hour, and/or aquarium size.

Keep in mind that most filter manufacturers state a larger capacity than what is realistic. As with the tank itself, it is also here better to buy too large than too small.

Fry are more sensitive to the water quality than adults.

Substrate

Fish feel safer with dark gravel beneath, and a dark backdrop to the tank. The gravel should be lime free. It is safest to buy it at the pet store (it doesn't normally cost much), and clean it in water before putting it in the tank.

Normal aquarium gravel (3-5 mm) or sand is generally the best alternative for Betta aquariums. Fighting fish are from nature's hand adapted to a soft substrate (mud). You can also have a bare bottom tank, the fish won't mind. This is used in fry tanks, as it makes the tank significantly easier to clean.