Yes, they need a tropical tank with filter, heater and light. 70-79 degrees is optimal for most tropical fish. I kept several neon tetras for years, they are mellow and easy to care for but tend to die if you do not take good care of the PH and parasites. Other breeds are hardier, but they can do fine with not too much fuss. I don't suggest any tanks smaller than 10 gallons. The rule is one inch of fish per gallon of water.
Yes. They require a regulated moderately warm tank, being Tropical Fish. The more stable and constant the temperature, as in the lest amount of difference between high and low, the less likely to have health problems such as Ick. 75f - 78f is ideal.
fresh or saltwater
no a tetra fish has a shiny streak
Many tetras prefer soft and acidic water.
Depending on the fish, it might be aggressive towards your tetras and mollies, which tend to be pretty passive fish. I wouldn't, just to be safe.
You could put the following: 3x Neon Tetra or... 1x Betta
Horse Isle Answer: Neon tetra
Guppies ,mollies ,neon tetra, etc. about 3 each.
It depends what kind of tetra but mainly all do
Assuming that you are referring to neon tetras, there are several brands of commercial "Tetra Flakes" that can be bought at nearly every pet store. I believe that there is also a pellet version of "Tetra Flakes".
all fish lives in water
5,666
Depends on the fish.
Provided you have sufficient space/water to house another fish. (A Platy needs around 2 gallons at least.) another of the same species or of a peacefull species like Rasbora, Danio, Tetra, Barb, etc will be OK.