How often have you been doing water changes? You may need to test your tap water if you have been doing water changes often. And just to warn you, eventually these goldfish are going to get BIG and will need appropriate housing. I tried keeping one goldfish in a ten gallon once, when he was small like yours, and was doing water changes every couple days, just to keep nitrates under 20.
Swim bladder problems are not only related to what types of food but also how much food you feed to the fish. I would try not feeding them for several days and then feed them only a couple small shelled peas after that.
Swim bladder problems are not only related to what types of food but also how much food you feed to the fish. I would try not feeding them for several days and then feed them only a couple small shelled peas after that.