You can feed them a little. That ammonia is very low and you will want a little bit to produce to move the process along.

How big are the fish? The size of the fish will determine an adequate feeding schedule. Fish are all too commonly overfed. Some fish will continue eating when their stomachs are full and they will poop out undigested food. It's the same as having overfed and having the food float around. It will produce tons of ammonia; so, be careful.

Are you getting feeder goldfish from the store? That may be the problem. You bought sick fish, which is not all that uncommon. They don't take care of them because they consider them the swimming dead just waiting to be purchased and fed to another pet.