You can set this tank up similar to how you have your normal tank set up. Just keep in mind that the water will need to be soft and kept at a specific temperature and acidity in order for breeding to happen.

get a tank thermometer to monitor the water temperature. test the pH of the water daily using pH test strips (available at pet stores) mix one part tap water with three parts reverse osmosis water to make soft water for your tank OR use fresh rainwater

You may even want to cover the back and sides of your tank in dark paper to block out excess light.

Female tetras tend to be wider and fatter than male tetras. Some breeders also claim that male tetras have a straight stripe and females have a crooked stripe. [4] X Research source

Allow the fish to stay in the tank for a day or two. Tetras should spawn after being kept in the tank for about one to two days.

Changing the water softness seems to trigger spawning because it mimics rainfall. Try adding a large amount of soft water to the tank if your neon tetras are not spawning after a few days.

The baby tetras will look like small splinters of glass swimming around the tank. [8] X Research source

To keep the tank dark, you can cover the entire tank in dark construction paper or use a piece of cardboard to block out the light. [9] X Research source You can use a dim flashlight to look in from the top of the tank during feedings, but be brief when you do so.

After a few days, you can start to feed the baby tetras baby brine shrimp as well. You can buy baby brine shrimp in pet stores.

Keep in mind that some of the tetras may die no matter what you do. Baby fish are more prone to disease and more sensitive to injuries.

For example, if you have a 50 gallon (190 L) tank, then you can have 25 tetras in your tank.

You can also try calling your local pet store to see if they are interested in purchasing some. Just keep in mind that pet stores only pay between $0. 11 and $0. 30 per neon tetra, so you will not make much money unless you sell in large quantities. [13] X Research source