The easiest way of providing for fry is to buy the liquid fry food from your local fish shop which is not expensive - they sell different sorts for all sorts of fry and you just squirt it near them with a pippette or eye dropper. However if you want to have a go at growing some infusoria here are some instructions
You'll need a large jar and some tank water. Its good if you have an established tank that likely already has significant numbers of microscopic lifeforms living in it. Add to the tank water some organic food, such as cut grass, a rabbit pellet, or blended lettuce.
Make sure that the culture has easy access to oxygen, and place the jar in a sunny spot. Over the next three to four days you should see the water go cloudy and then clear once more. You will want to wait until the water has cleared, as this is the sign of a successful and 'clean' culture. Once you have clear water, add a little to your tank to feed your fry.
How you do this depends largely on your personal preference and what works for you. Some people recommend a slow siphon method that supplies a constant stream of fresh infusoria into the tank. Others recommend simply tipping half the culture into the tank. This is slightly more risky. It's important in either case to ensure that the organic matter does not end up in the tank. Then you'll simply have rotting organic matter in your fry tank, which can cause all sorts of problems.
