First, I wouldn't expect to sustain a pipefish on cyclopeeze or any other single prepared food. Even if it's accepted, the fish will need more variety than that, which most likely means pods.
Also, your sixline is not aggressive toward its current tankmates, but might be to a new arrival, especially a passive fish like a pipefish.
Honestly, I don't mean to be so negative, but I've tried and failed to keep dragonface pipes in a 20 gallon. They were eating tiggerpods and cyclopeeze. In the end, though I just think the tank wasn't big enough to sustain them. I know you're talking about a different type of pipefish, but it's really not a good feeling.
Finally, what other two fish are in the tank? I thought you said the tank had one false perc and one sixline? Are you moving the sixline and clown into your prop tank? If so, maybe you should leave them where they are and just devote the prop tank to a single pipefish. A pair of bluestripes would do great in a tank like that. I don't know about a banded pipe.