You'll need two 1-liter bottles, an air pump, a lamp, flexible airline tubing, rigid airline tubing, brine shrimp eggs, baking soda, and salt (kosher salt, canning and pickling salt, rock salt, or any non-iodized and additive-free salt will work fine).
Carefully cut the bottom 1-2 inches off of one bottle and discard the bottom piece. This will be inverted to become the reservoir to hatch the brine shrimp in. Brine shrimp hatch best when they are continuously circulating, so the inverted bottle is a good shape to hatch brine shrimp in because there is no bottom surface for them to settle on.
Next, carefully cut the bottom 6 inches off of the second bottle and discard the top piece. This second bottle will become the base for the hatchery. Put the two bottles together so the second bottle supports the first in an upside-down position. And if you like, you can tape them together for extra strength.
Cut a length of rigid airline tubing to roughly the same height as the reservoir bottle and attach a length of flexible airline tubing to it. Attach the other end of flexible airline tubing to an air pump. The rigid airline tubing should be placed into the hatchery reservoir so that the end of it is right at the very bottom of the bottle.
Fill the reservoir about 4/5 of the way full with warm tap water. There is no need to use dechlorinator. Turn on the air pump. Add 1 level tablespoon of salt and just a pinch of baking soda (to help keep a stable pH).
Now you can add your brine shrimp eggs. Make sure you buy eggs with the best hatch rate you can afford.
Turn on your lamp and position it directly over the hatchery. This is done because; a) brine shrimp need a constant light source in order to hatch, and b) it also helps heat the water so the brine shrimp hatch faster. If kept at 78-80 degrees F, after about 24 hours the brine shrimp should all hatch.
Check back in 24 hours... you'll know the brine shrimp have hatched when the color of the bottle turns orange from the color of the brine shrimp themselves. At this point, turn off the air pump and allow the hatched brine shrimp to settle to the bottom of the bottle. If you position the light source so that it's aimed right near the bottom of the bottle, the brine shrimp will settle to the bottom faster because they're attracted to the light.
Remove the brine shrimp (and avoid the egg shells) by using a turkey baster to suck them up directly from the bottom of the bottle. Alternatively, you can use a straw by placing one finger over the end of the straw and putting the straw right to the bottom of the bottle. When you release your finger, the straw will suck up the water right from the bottom, bringing the hatched brine shrimp along with it. Place your finger back over the end of the straw to transport the brine shrimp to the fry tank for feeding.
Rinse out the hatchery and start the process over again. In fact, it's a good idea to start a second batch 12 hours after starting the first one so your fry can have a fresh meal every 12 hours.
I also have a video that walks you through each step. Check it out below!