I too often use stronger currents BUT I would not advise it. Are they being tossed around? If so, reduce the pump. They will become very stressed if it's too strong. Try adding some sort of baffle like wood or plant - anything that will reduce current and provide rest area for fry.
Pellets usually have a more balanced nutrition. Try feeding them more worms than pellets. Worms contain more fat and usually will boost more growth compared to daphnia, mosq larva or pellets. Remember to be patient. They will not grow over night, but they will eventually grow. . . . As far as I know they keep growing until 1 year (at least).