Strange behavior...probably dying

[fstar25]

I have a blue-green chromis that was my first fish and has been in my tank for 8 months. last night he was swimming around after lights out which he never does and he was swimming vertically (tail towards sand head towards top of tank). I check his little sleep cave and nothing was in there so I tested my water. Ammonia, nitrates, nitrites all 0 and phosphates about .008

Well, I didn't post last night because he went back in his cave and I thought he was fine. This morning before lights on he was out again and swimming vertical. I caught him and put him in quarantine but I'm afraid he's not gonna make it. There are no visible signs of damage on him, no spots or stripes or lines of any kind that haven't always been there.

Any ideas or directions I should be looking?

Thank you

 

[Flyfisherman]

Tough to lose your first fish. I would leave him in tank, quarantine going to stress him even more.