Copper is a toxin that I would only use in the rarest of cases (velvet infections of fish I can’t use CP with). It is not really good for fish....
At the time of purchase, the fish had come into the store the day before and seemed alert and was interested in food. Two sales people told me it was from a Los Angeles wholesaler, but wouldn't give me an actual name. I was reluctant to buy, but since they are also a BAR sponsor I decided to take a chance.
FYI, my main system has been running for ten years and is setup for SPS, if my water parameters are good enough for Acropora, it's good enough for any marine angelfish. I also have success and experience keeping dwarf and large angelfish, and all of mine readily eat pellets and other prepared foods from my fingertips. And finally, Queen angelfish are considered very easy to keep, not finicky nor shy, and have a strong constitution. For the first week I quarantined the Angel in an established hospital tank running copper then praziquantel. It was fed pellets, frozen, and live foods, it ate a little but continued to loose weight. Worried, I moved the Angel into the refugium last week to feast on live sponges, macro algae, soft corals, and Copepods the size of adult brine shrimp, but to no avail. It was grazing, but became more emaciated, today it was struggling with the weak current, barely hanging on to life. My educated guess would be that this fish was collected from the wild with cyanide or some other toxic chemical, and then sold to unsuspecting fools like me.
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Praziquantel is known to impair a fish’s appetite, one of the reasons why I don’t use it as a prophylactic treatment.
Also, one week of treatment won’t do much and that “rescue move” into your main system (assuming the refuge is not isolated) has now put all your existing stock at risk to catch whatever this fish died of.
As for a Queen Angel being cyanide caught – educate yourself! There is no cyanide or other poison fishing in the Caribbean.
Any live fish is a risky buy – always! Captive bred fish included!
BTW: Queen Angels are likely to nip on SPS and LPS, so this fish dying may have saved you a lot of grief (assuming you didn’t contaminated your system with a disease)