hahaha, I've never thought of feeding the napa cabbage to my fish... and definitely wouldnt feed the kimchi to them either
Napa cabbage also is good in soup
But on topic, I fatten up my tangs with nori soaked in selcon and garlic. Personally, nori is so cheap ($0.99 for a hundred sheets) that I have never considered feeding my marine fish a terrestrial veggie. Plus, all of my herbivores have gone nuts for the stuff (nori), soaked in garlic and selcon or not.
I use the pvc trick as well, except my method is a bit different. I cut my pvc pvc so it will hang on the edge of the aquarium and stick about 5" into the tank. I then took the plastic mesh from my DI filter and cut it down in size till it just covers the pvc pipe.
I wrap the nori around the pvc, then I wrap the thin plastic mesh around the nori, then I rubberband it all in place. Doing this stops the fish from tearing big peices of the nori off and then leaving it to float around the tank. With the mesh in place they nibble off what they need without wasting so much.
Not my idea, I read it somewhere else. Cant remember where tho. I also feed my tanks at least twice a day with mysis or other frozen food mixtures (like frozen formula one).