You should have left him in the main tank as you will need to treat the main tank as well as him. The main tank is infected with ick and will need treatment or once you put him back in the main tank he will contract ick again. Ick eggs live in the substrate so impossible to get rid of it without treating the main tank.
I would do your rounds of ick treatment first.
Then the other treatments I have done are metroplex soaked food, and a round of prazi pro....I’ve done both of these treatments when my EBJDs stopped eating and it always worked well for me. I think in the beginning I done two rounds of ick treatment, and three rounds of the prazi pro and metroplex....I have noticed it slows growth tremendously when they decide to stop eating.
In addition to those treatments I would feed frozen foods, they would never reject frozen foods...mysis shrimp, broke shrimp etc...might not be the best diet but I always figured something to eat is better than nothing to eat....