My Festaes ate Massivore Delight, Supirulina flake, garlic, and frozen Krill, a varied diet is always best. They were fed daily in the morning then lights out til evening.
Good growth rates aren't just about food tho. Water quality - low Nitra via overfiltration, regular water changes, and cleaning, increased levels of dissolved 02
thru powerheads, circulation, and surface agitation. Water volume to put the ppm on your side and the ability for the fish to roam. Alpha status, competition within the tank by having multiple juvi's, and Mother Nature - genetics and sex - Alpha males grow fastest, sub males second. Alpha females 3rd - all play into it.