Hi Jay, thank you so much for the suggestions! The fish in the tank are: Fiji puffer, Valentini puffer, longhorn cowfish, algae blenny, Tomini tang, and a six-line wrasse. They seem to be able to get along and I have not observed aggression. The weird thing is that all of these fish were in a quarantine tank with Copper Power for a month, before treating with prazi etc, before moving into the brand new display tank. They were good in the tank for about 1 week, before fungus like growth (white & fluffy) starts to appear on the longhorn cowfish and the tail on the Tomini tang. After treating with Kana & Metro, plus general cure, the fungus seems to disappear but then the white dots starts to appear. Now they are all being treated with Copper Power again (2.3ppm) and this is a fish only tank. Today, the damsel seems to look better but the longhorn cowfish has got weird stuff on its fins again (please see image). I am very confused... Any help is much appreciated! Thanks again!