[Felicia]

From what I understand, the reason freshwater foods are not healthy for saltwater fish is because the freshwater animals do not contain as much HUFAs, or Highly Unsaturated Fatty Acids. A saltwater fish fed only a freshwater diet will die of fatty liver disease and malnutrition.

I don't think much is known about feeding freshwater foods to saltwater invertebrates, but it doesn't seem to be too much of a concern to me, especially if it is done sparingly.

And don't worry, it does take a while for an anemone to completely "swallow" its food.