got the following info in this link:
http://www.bettas.org.uk/forum/index.php?page=12
Introduction
Infusoria is the very smallest of all live food, you cannot see it without the aid of a microscope but it is invaluable for raising the smallest of fry like those of Tetras, Gouramis ect. Infusoria is the name given to a whole range of single celled animal and plant organisms which feed on bacteria. A new culture of Infusoria can be prepared and ready to use within four days so a little forward planning will be called for if the culture is to be ready for a batch of new fry.
Starting the culture
Start off with a freshly cleaned small aquarium of one too three gallons and fill it with old tank water. Use an aquarium heater to keep the temp of the water at 80F and keep it lit for 24 hrs per day and keep the water very strongly aerated whilst the culture is growing, this will ensure the culture will grow at its maximum speed and keep it healthy.
In order to start growing the infusoria will need a supply of food in the form of bacteria. In turn these bacteria will need feeding in order to build up sufficient numbers for the culture to be a success.
Using meat or fish will result in a smelly cloudy solution so it is advised that only vegetable matter is used to begin the process, a small piece of boiled potato about a half inch cube in size or a couple of wilted lettuce leaves both work well along with a few drops of Liquifry fry food which encourages the growth of infusoria.
After a short time the water will turn cloudy, this isn't the infusoria but it is the bacteria. It is important at this stage to keep the water well aerated or the bacteria will use all the free oxygen and inhibit the growth of the infusoria.
Once the water clears it is ready to use, it will be full of infusoria which can only be seen with the aid of a microscope.
The culture will usually last for about seven days and then start a new one using some of the water from the old culture to inoculate the new one which will speed up the process.
Feeding guide
Because the infusoria culture water may contain either or both ammonia and nitrite and new born fry are extremely sensitive only very small amounts of the infusoria rich water should be added at a time. An eye dropper can be used to place just a few drops every hour in the fry tank or a siphon can be set up using a piece of air pipe and a valve to restrict the flow so that just a few drips are released every minute.
The flow should be checked on a regular basis to make sure that it keeps to the right rate. As with all food make sure that you don't over feed the fry or you risk fouling the water and losing the brood.
here are some more links:
http://www.cichlid-forum.com/articles/fry_food.php
http://forum.aqua-fish.net/?topic=infusoria-great-fry-raisng-food-how-to-grow-it-
http://davidcecere.pipidae.org/infusoria.htm
http://www.guppies.com/forums/showpost.php?p=195656&postcount=3
http://www.1911encyclopedia.org/Infusoria
