Most common use: Fry

Infusoria is a general name for the very small life in water, like paramecium protozoa, rotifers etc. The infusoria is fed on decaying organic material such as old leaves, grass, hay, vegetables, milk and much more. Actually just what comes to your mind.
When the fry is very small it can be a problem to find small enough food. Infusoria is the perfect answer here and you can easily make it.

Examples of making infusoria:

If you have Java moss in your other tanks just put this into your fry tank. It is full of infusoria and will deliver good start up food for at least a couple of days. You will need to add some food later on but as a starter this is a good solution.

Take some tank water into a glass jar. Add a few old leaves from the garden and eventually some grass. Place it in a sunny area outside or in your window for a couple of days and the infusoria will start to develop. As the Infusoria is so small it is difficult to see them in the water. But if your water turns cloudy or green you have a good infusoria culture. Use an eye dropper to move the infusoria from the culture to the fry tank.
A flashlight and some good eyes might will allow you to see some of the micro organism but it can be difficult. If you have a microscope you will see them easily.

Put some lettuce leaves in a glass jar enough to fill the bottom of the container. Fill up the container with very hot but not boiling water and let it cool down to room temperature. When about 20-25 degrees put a lid on the jar and wait some days. Then you will have a heavy growth of infusoria. Use an eye dropper to take infusoria from the jar to the fry tank. Please note that old lettuce is better than fresh lettuce as it decays faster.

Remember that infusoria is only a starter food. As soon as the fry is big enough to eat other food they should be offered this.