I take a couple of pea sized chunks of dry cat food and crush them slightly. These go into the bottle along with the hottest water from my tap. Put some polyester stuffing or filter floss in the top to minimize other air born microbes from entering the bottle. This is put on the shelf for 24 hours to allow the cat food to break down and the nutrients to dissolve into the water. At that point the container is inoculated with paramecium from the starter or an older culture. Place it in a location without bright light.
I use hot tap water because that helps break down the cat food faster. I have well water so I don’t have to worry about chlorine or other chemicals added to city water from killing the paramecium. If you have chemicals in your water you will need to treat it or allow it to sit for a few days until they are gone. One club member uses distilled water with good success.
After 4-5 days you will notice the water is a bit cloudy with the infusoria. If you hold it up to a bright light you might see small white particles. You might need a magnifying glass because they are so small. These are the individual paramecium.
I use a turkey baster to extract a couple of teaspoons of the culture. Slowly drip this over the air tube of the sponge filter. The bubbles help get the paramecium mixed throughout the aquarium where the fry can hunt them down.
The cultures seem to peak after a week or ten days and it is best to start new ones every week or so. If you forget and the culture becomes clear with no paramecium visible you can usually jump start it by adding a couple more pieces of the dried cat food. Most of the time you will have a good culture going again in a week, but it is best to start a new culture at that time.
Culturing paramecium is a good way to provide infusoria for tropical fish fry that need very small foods at the start. The toughest part may be to find someone to give you a paramecium starter culture. Check with the serious breeders at your local aquarium club.