DUDE!!! You are so in my brain. I was just talking to my wife about doing this today...Been contemplating it for a few weeks now. Looks good! I'm still considering.
They probably just need to re-adjust. They should be ok. My female motoro does that when I stir and/or remove/add gravel after water changes but she eventually calms back down. I added gravel from another tank when I left for a few days so that the black worms could bury themselves and the rays could forge them out while I was gone. This was the first time I did that and I was gone for four days and it worked! All my rays (including the new lil hystrix) was perfect when I returned. (That beat having my neighbor watch/feed them...Last time I did that, I lost 3 rays and almost quit fishkeeping because I was so heartbroken).
Anyway, I digress. Your rays should be fine but if you're worried, test your params.
Niceee, sorry want to ask, the first aquarium with black gravel, I want to know how to clean the gravel??? i want to use small black stone, its about 0.5-1 cm stone size. thanks