Tascam Guitar Trainer

I have a 55 gallons tank and four goldfish. A male fantail 3", a female panda oranda 4", another oranda not sexed yet and my favorite the peaceful black more 2". They have been living in harmony until two weeks ago when the fantail decided to chase and nip the black moor. No injuries in my black moor so far only descoloration on his sides. I was a little concern and thougth to give away my fantail, he has dots on his gills prove of his sex. The fantail does not attack the orandas at all only the black moor. I wouldn't like to get home and find an injured blind fish. My aquarium is heavily panted and the moor finds shelter easily. Should I remove the fantail from the tank?