One of my goldfish isn't eating, should I seperate them?

[Civitello]

I have a partially cycled tank with four young goldfish:

pH 8, NH 0.25, NO2 2, NO3 5, Degrees C 19.8. Salt 1 TBSP/3 Gal

20 Gallons (soon to be upgraded).

The smallest goldfish (Currant) has been observed eating exactly two bites of food over the last week and is not growing. The others are eating and growing.

I have observed one of the fish attacking Currants caudal fin one one occasion and another fish biting at Currants side. Currant spends all their time near (not at) the surface in the same area of the tank or hiding. Currant has the ability to swim quickly and get up and down just fine.

I tried switching to pellets from flakes with no change.

I tried separating Currant in a container of aquarium water floating near the surface during feeding time, but they did not eat. Perhaps I did not wait long enough?

I have a smaller aquarium that I could put Currant in to give them a chance to get comfortable, eat and grow some. Should I do this?

 

[Aiken Drum]

Yes. Seperate the fish.

Sometimes bullied fish just give up trying and will eventually just die. To give it a chance i would isolate the fish and hopefully given time it will recover and start to eat.