Hey Dmorty,
I'm not sure if that explains my question. Few months ago I pick up two very tiny hippo tangs (hepatus). I was surprised because I often see fights between this two little guys in my big tank. I thing if I introduce them in my small tank like the polyzonas I have to divorce them also. In big tank it is definitely easier.
Bad news. The polyzona from the video disappeared. Yesterday he was very present and catch Nori from open water and pick algae from the stones. S**t!
The smaller one in small tank eat very well and get thicker the last days. In the small tank I feed 6 times a day different small frozen food and pellets. Also the water speed is less and the food cycle long time slowly in tank. Also I have enough nori on clip the hole and no pressure from other fish. I will recognize the development of that last fish the next weeks and decide again to buy more of tham or stop with polyzona.