Ocellaris behavior after ritteri hosting

[Ryengoth]

My pair of ocellaris have been together for a couple years and were maybe a year old when I bought them, about 1" long at the time. I finally have the space for a ritteri, put one in a few days ago and they hosted it within a few days and stay there most of the time now. One seems to hang out in the tentacles and the other roams around more during the day. That one will swim by the other, stop and flash/shiver it's body, facing sideways. Is this a mating behavior or something else? I could find nothing about that online, just fast swimming by the female and rock clearing for the bed.

 

[Ryengoth]

So... based on another thread my pair is likely establishing a mating. I'm not sure how I'm going to make a rearing area with a stacked wall reef setup. It should be near the nem, right, but shaded from the light.