You have a Powder Blue and a Gem so more than likely one of them is slashing your Tomini. I have three large Tangs and usually when they go at is at night, so you don't see the damage until the next morning. The cause at least for mine is squabbling over sleeping spots. A new Tang will pick out a spot in a Rock Crevasse and usually it is already claimed by one of the established ones, so a fight occurs. My 3 each have a spot they go to every night so you can see how a new one could cause problems. You could try making a new spot or two that may help.
Post another Video with a broadside shot and let's have Jay take a look. After all, he is the Doctor.