Culturing rotifiers in the breeding tank itself is sometimes possible but mostly a highly uncertain Thing. You should in any case set up a separate culture.
In Germany, breeders mostly use a slight yeast suspension for boosting the rotifiers.
It’s still easier to set up a Paramecium culture. The most easy method is taking some small dried material of bananas. But it needs about ten days for Paramecium to develop. They need very little food; good is a drop of milk, mostly less.
Vinegar eels are also taken rather early. And if you are lucky to get cysts of the very tiny Artemia of the Californian lakes, the young Paros might tale them from the very beginning. But quite freshly hatched only. Two days old they are much too big already.