I've had my tanzaniae since the middle of October. I kept a constant supply of feeders in his tank until I decided to break him two weeks ago. In the past two weeks, he has grown more than in the entire two months before that.
Using the cyprinids that are commonly available as feeders is not a good idea. They are nutritionally devoid, they harbor diseases and they have thiaminase. If you have access to a ready supply of cheap, quality feeders, such as the dojo loaches used in Japan, feeding live is OK. Feeding your fish these cyprinids is especially counterproductive if you wish to put on mass.