Rotifers only live 8-12 days. But they reproduce expotentially in the right environment. They need to be kept at 78 and in green water (Nannochloropsis) for this to happen.
If you want to keep a culture, it is best to keep them in a bucket with an air bubbling at 78 degrees and keep the water a green tint. They also have to harvest them daily after the culture takes off.
Here's a link on how to maintain a culture: Culturing Rotifers At Home