Fry growth is dependent on two things, water and food.
Food: 1fish2fish created a thread on fry food. I personally use infusoria and Baby Brine Shrimp. Infusoria is added to my tank a few times a day starting the day fry become free swimming. I also have a 2 brine shrimp hatcheries at all times. One started 12 hours after the first. I feed brine shrimp from the day the fry become free swimming to about one month. At this time I keep adding some Baby Brine Shrimp but I also add in a little frozen bloddoworms and eventually stop brine shrimp all together.
Water IMO is more important than food. New breeders rarely change their water enough to support large growth. As soon as dad is out I feed the fry. The next day I get a 1/2 gallon jug of condtioned water and put it in the tank (careful not to trap fry!!!). It stays in there for an hour and then I gently pour it in. I do this until the tank is full and since I use 5 gallons (works better for me) the tank is full in no time. The next day I take a long piece of airline tubing and attatch an airstone to the end (so I don't suck up fry) and take out at least 50% of the water. I replace it by floating the 1/2 gallon jug in the tank for an hour and pouring it gently in (just line when I added water). I do this everyday until week 3, then I increase water changes to 75% daily. At one month I put my fry (in groups of 5 to 7) in 16 oz plastic cups and float them in the growout tank. Then after a day or so I release them. Make sure not to leave fry in the spawning tank!!!! Then I change 75% of the water in the growout every 2 or 3 days. I do this until they become aggressive with each other and then I jar them.
Massive water changes takes out a hormone the fry produce which stunts other fry.
Good luck raising your fry :)