You can crush up the pellet/flake you have--make sure it's finely crushed though. I've heard people give brine shrimp too.
I keep my tank 80-82 deg F (a little higher than main tank (78)) to speed up growth. They eat more though, and create more waste.
I'll do water changes three times a week (approx. 50%). Usually, the fry almost double in size each week up to a point. The bigger they get, the slower they grow (or maybe it's because they start so tiny it looks like they grow faster ) I have mine in a 10g, so it's not hard to keep up the WCs.