Fenner gave great fish advices.
68 is still young I think. 85-90 is the going marker now.
I don't think you actually check out in your sleep.
You probably get a big jolt with a lot of pain on the way out.
I am a fan of ozone. I use both UV and ozone together, too. Ozone is great for water clarity. I have both redsea and Poseidon but redsea is my go to unit due to efficiency. I flush it out with water to recharge the unit on a yearly basis.
Beautiful yellow tang.
Yes, my tangs are pretty aggressive and has nothing to with being outgrown in small tank. Wear gloves to be on the safe side. But then it's a good excuse to start planning for an upgrade.