Sadly I lotst the copperband, but after 2 X 50% water changes things are looking better, all fish feeding except blue cheek goby who is not looking well.
All things considered (had another spike of ammonia, nitrate, and nitrite) loosing two fish doesn't seem so bad.
As far as the box fish goes, he never looked stressed! was still waiting to be fed twice a day. He is used to my hands going in and out and comes to investigate what I'm up to.
I have upgraded skimmer to Vskim600, and also have external canister filter - fluval 405, with floss, live rock and poly filter.
I have added some pure marine pearls too.
I think the copperband was one step too many for the original filtration system, but to be fair everything had been happy up til that point.
Decided to upgrade so it doesn't happen again, if I add any more fish.
I agree the copperband is a difficult fish - it was a bit of an impulse buy. We all have to learn though.