Pincushion urchin flipping upside down??

[jpmwjm]

I have a purple pincushion urchin. It has been in my tank for over two years. About three days ago I found him on his back. I flipped him over and he has a area where he is missing some spines and a little darker purple. Later that night he flipped back on his back. I righted him again and he moved around that night and the next day he flipped back upside down . I waited a few hours to see if he would right himself. I flipped him back over last night and he again crawled around the tank a bit. Today he flipped once again. I just righted him once more and he is crawling again. I checked ph it is at 7.6 Kh is 7 nitrates, phosphates both showing zero... Had started doing small vodka dosing a few weeks back to try and help with green and red turf algae. Currently dosing 1 ml a day on 90 gallon total volume system. All other fish and inverts doing good. Kenya trees and shrooms opening real good. I'm hoping the urchin incident after two and a half weeks of vodka dosing is coincidental. Will they flip over to heal sore spot if hurt somehow? He seems to flip over to same spineless area each time.

 

[Betta132]

Could it be he's falling off of things and settling on the same spot due to the lack of spines there? Could something be flipping him over, maybe some form of intelligent fish trying to eat him?
Has salinity fluctuated at all? Urchins don't like that in the slightest.