I have 4 discus. One has always been smaller than the others and doesn’t seem to grow as fast.. In the last two days, I have noticed he is swimming alone and is not eating. What could be wrong with him?
She is sick and not feeling well.
Most likely she has been bullied.
Put her in special tank.
Treat her with Epsom salt for 24 hours,
Then change water, treat her the Epsom salt again for 24 hours.
On the third day feel her some live food.
She will eat.