It took me 6 months to train mine he was near death in my 33 with 20 g sump with 60 lbs of live rock ( no swimming room lol ) he was a blue dragonet . Used chemiclean and the frozen just wasn't enough he died. Even when there on frozen they are grazers and need to be fed every few hours a tiny bit . So having a huge aquarium is the best.
Iv heard of using a little container , poke a few holes in it . And hatch brine shrimp and they will swim out of the holes . Never used it though .
The best time to feed was when he was hunting the sand bed in the back . Spray some mysis and not watch . They no when your watching! Eventually they will flap there fins and make the mysis swim sucking them up in the water
Goodluck