feed them a variety of food this will help them grow. Try pellets aswell as flakes, brimpshrimp, bloodworms(have a lot of protein so as a treat its fine) either live,frozen or dried. Help them digest their food by giving them veg, like broccoli,cucumber,peas. Fancies also like to bottom feed so where possible if you feed flakes push them below the surface so they sink. This will help Goldfish avoid swimbladder problems which fancies can have problems with as they get older.