Sick or love sick?

[Dojo]

I had a Golden Dojo Loach who lived with platys for quite a long time. Finally I got a 29G long and a week after it cycled added three tiny Golden Dojo loaches. Two of them were bonded from "minute one" and they seemed to have ostracized the third one. After 4 weeks of quarantine I added the oldest and the largest Dojo to the tank. He/she bonded with the smallest one and all was well, except the third dojo did not seem to grow as fast as the others two.

About a month ago I had a nitrite spike and the oldest Dojo did not make it. ( He had a lot of bloating issues in the past and did not recover the way the other three did. ) Since we lost the oldest loach the little one refuses to socialize with the other two even though they keep trying to engage him, and, most importantly, he stopped eating. He does not eat even when I drop a pellet right in front of him. I don't think he had a bite off his pellet for at least 5 days. He has been hiding in a tunnel and comes out only when I nudge his tunnel gently with a long chopstick. Even two weeks ago he would swim all over the tank by himself, but he swims no more. Because the other two have been growing steadily he seems totally emaciated and his head is visibly smaller than others', although all three are about the same length.

I am worried that my third dojo may have gotten whatever the oldest one had and may infect the other two. What to do?

[Loachloach]

Not sure about dojos, but generally with loaches 3 is not enough for that same reason because one of them, or two can bully the third one. You are better off keeping them in 5+ numbers.