Sick ocellaris clownfish

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I have had a pair of small captive-bred ocellaris clowns for 2-1/2 weeks now in a 20 gallon quarantine tank. These are my first SW fish.

One of the clowns has always been active and lively with a good appetite. The other one has never been as good an eater.

In the past few days the one clown has stopped eating. I noticed some cloudiness of the clear part of his fins, and a vague milky/transparent film over the shoulder area of his body behind the head.

Prior to putting these clowns in the quarantine tank I did a gradual acclimation over about 90 minutes. Then I gave each clown a 15 minute formalin bath with aeration before release into the q-tank. I have been running hyposalinity in the q-tank as described in the clownfish article here for prophylaxis of ich.

Today's tank parameters are:

temp 79.5 degrees
pH 8.0
ammonia zero
nitrites zero
nitrates between zero and 5

So any advice on what to to? Does the clown have brooklynellla and should I do a repeat formalin dip? Should I raise the temperature, or bring the salinity back to normal?

I have tried feeding flake and frozen home-made food, I have even offered some of my FW live food, the other clown eats it all up but the sick clown won't touch it.

The store I bought these clowns from does not keep their captive-bred stock separate from their wild-caught specimens, and it does run some copper in the water. Two other clowns I picked up for a friend at the same time are doing fine last I heard.