Sometimes, fish just die. If everything else is doing ok, I wouldn't worry about it. You are going to have losses in this hobby.

AquaAddict

If your water parameters are good (Nitrate, Nitrite, ammonia, phosphates) and everything else is doing well it could be a one off.

Yea what he said. After everything you posted it sounds like no problems. Continue reefing $hit happens

Amen brother. We win some we lose some much more often, that is reefing. It's not for the feint of heart for sure. The loss of any critter in your care is always a bit upsetting but on the bright side clowns and 6 lines are easy to replace. Could have been an Achilles. I too have had fish simply vanish for reasons unknown. If there are no signs of stress displayed by other fish, and rock solid perams the odds are good that S##t happened.
Be cautious, watch the remaining residents, and hope for the best. Just don't beat yourself up, and whatever you do don't jump to conclusions and start trying to do too much to your tank. Until you know what the issue is, you have no direction for action and action for the sake of action can have serious effects on an otherwise healthy or stable tank.

Well almost a month and everyone else is thriving and happy RBTA split and one of his previous splits split clown fish seems a little sad and moopy without his friend but he still eats and roams the tank every now and again the other inhabitants seems to be thriving so I guess I will just keep an eye on things for now and continue on.