Infusoria is the general name given to a whole host of micro organisms found in any body of water containing vegetable matter. In a fish tank, it is seen as a cloudiness of the water and can be of great value when trying to rear extremely small fry. Infusoria can be the difference between raising 90% of your fry or a few weak specimens.
Infusoria is very simple to cultivate and it is well worth having a constant culture on the go in order not to be caught on the hop by a surprise spawning of that hard to spawn fish you have been trying very hard to breed.
Lettuce leaves are suitable for starting a culture, as are potato peelings. Put the leaves or peelings in a glass container that will hold around 2 gallons of water. It is best to use water from an established tank and also to bruise the lettuce leaves as this will speed up the process.
Place the container in a warm, semi-dark place and after about 4 days you should have a nice culture of Infusoria. If you hold the container up to the light, you should be able to make out the tiny creatures moving about. The water will be cloudy, but it should not have a foul smell at this stage.
If you have a lot of fry to feed, the best way to do so is to draw a pint or so of culture rich water from the container and pour it straight into the fry tank. Another way is to siphon some into the fry tank whilst suspending the container over the tank somehow. Using a valve at the end of the length of airline siphon will allow good flow control. When the water in the Infusoria container falls fairly low, simply top it up again with tank water.
Even the smallest fry should only need to be fed Infusoria for about a week. You should try to get the fry on to newly hatched brine shrimp as quickly as possible, as there is no substitute for brine shrimp. Not even Infusoria.