New to forum , maybe too late

[Flying Dutchman]

I would put the small one in the 5 gallon tank so it could gain some weight. The big one is clearly the dominant one and the small one doesn't want to and up as food for the big one, that's why it isn't eating. Just my thought.

[ravensgirl]

I agree in any community situation if there's an animal not thriving as much as the others then it's worth separating to try and give them a chance to thrive.

Welcome to the forum!