[Myka]

Fwiw, API are perfectly fine test kits. I have found them to give very similar readings to Salifert and Elos.

The description of the dying fish makes me think that the fish either had Brooklynella or Marine Velvet. It would be odd though if the new fish did not pass this on to any of the existing fish. Wild Clownfish are very susceptible to both of these diseases as are Pigmy Angelfish to a bit lesser degree.

I suggest setting up a quarantine tank for new fish so that there is much less risk of a new fish introducing a pathogen. Both Brooklynella and Marine Velvet tend to be VERY contagious.

I also suggest buying captive bred fish whenever possible. In my opinion, there is absolutely no reason for a hobbyist to be buying wild caught Clownfish when they are mass produced as captive bred. You are likely to have much better luck with a captive bred fish.