Shrimp Dying?

[banditpowdercoat]

OK, I have tried a few times to keep cleaner shrimp and other shrimp and they seem to last 4-6 mos, then dissapear. Now I got this tank used. Not sure if there was ever any copper used in it? I have had the tank for 6 years now myself. Would the Salifert copper test kit show trace amounts from years ago? Also, other tank inhabitants are
Naso Tang
Hippo Tang
yellow Tang
Coral Beauty
Flame Angel(died last month with emergency tank teardown)
and a Brittle star

Had a GHA outbreak a while ago, That seems to be under control now. Also, A Lawnmower Blennie died and dissapeared a while ago too.
Had a tank leak last month so had to tear down and noticed no shrimp whatsoever. I did have 3 a couple months ago. They never really came out tho, Always were hidden in the rocks.