To start - add a starter culture to your jar (or whatever) of tap water. Use tap water or bottled water not aquarium water to prevent contamination. Add a few dry split peas - I use 3 or 4 in the half gallon bottles. Then add a small pinch of dry baby cereal. Continue to add the baby cereal daily unless the culture starts to smell bad. This means you've overfed. Just don't feed for a few days and everything will be fine. Add more peas as the old ones disappear. Within a few days to a week you will see a cloud of rotifers. These can be removed with a turkey baster or small siphon (a piece of airline tubing works well). Since they live in freshwater just put it right into the fry tank. The rotifers live until eaten.
Do not aerate the culture. They will do much better in "stagnant" water. It doesn't matter if your just using a small jar or a large tank. Also - no filtration. You'll just end up filtering the rotifers and their food out of the culture. The baby cereal and split peas that are fed to the culture "dec ...