You can try this web site. http://www.seafarm.com/rotifer/
To grow rotifers it is easier to use the concentrated algae like these. http://www.reed-mariculture.com/microalgae/
Nannochloropsis is usually the choice.
Depending on culture size a bottle can last months.
Many people use two tanks alternate cleaning every week.
each tank is cleaned and the culture restarted every two weeks.
also... I understand that as the culture reaches a high density, a certain percent of them must be harvested on a regular basis to avoid over density and culture crash.