Sudden death

hi guys really need some help on this one, i have a red sea max 250 set up as a reef tank and today very suddenly i had a chinese zebra bar goby die, i have in the tank with it, a yellow and blue tang, clowns a royal dottyback and a yt damsel there are 2 other chinese gobies as well. i tested my water and everything seems to be very stable and all the other fish are doing fine. i fed them same time as i do every day all the bar gobies came out and ate it was frozen brine and some nori. they ate both as did all the other fish. and about 2 hours later i was looking in and a bar goby had died. i have acans, a cataphylia, duncans, finger leather blastomussa merletti and a goni in the tank with a fungia and a clam the only thing i can think of is when it darted into a hole it missed and hit its head. do you guys have any ideas

 

could be accidental death. Your stocking list sounds like it could also be aggression. But the red sea max is a 66g tank (38 x 21 x 26.2”). You have 2 tangs, clowns a royal dotty and a damsel, these are all super aggressive fish. Especially with both tangs being too large for it. Also multiple gobies can be hit or miss, the ones you listed i read do well in pairs or groups. Perhaps, three was an odd number where two paired up and kicked the other out. Theres always so many possibilities when we just find them belly up.

Sorry for your loss.
Nick