Help! What disease is this?

[fishydr]

Sorry for poor photos. Lesion is behind the dorsal fin, Started like cotton wool, now ulcer like. Purchased 24 hours ago. Tank parameters good.

Lfs gave me a Protozoa treatment, but I thought was fungal and bought i icu/fungal treatment (Tri sulpha)

Any thoughts?

 

[ThRoewer]

A whitish layer on a clownfish is almost always Brooklynella.
This fish needs immediate treatment (see below).

Here are a few articles about Brooklynella:
1. Brooklynella hostilis and Uronema marinum
2. http://www.chucksaddiction.com/brookynella.html
3. Identifying Parasitic Diseases in Marine Aquarium Fish - A Hobbyist’s Guide to Identifying Some Common Marine Aquarium Parasites

The most effective treatment I found are formalin dips. Often one dip and afterwards transfer to a clean tank is enough to safe fish with early to clearly visible stages but if you want to make sure it is completely gone do dips every 3 days for 2 weeks, ideally done in combination with TTM to prevent reinfection (see 3. article).

For dips add 20 drops of formalin 37% to a gallon of saltwater (can be from the tank the fish is in), add an airstone or a small pump and then put the fish into this for 30 to 45 minutes (less if the fish shows signs of serious distress).
After the dip the fish needs to go into an uninfected (quarantine or hospital) tank.

 

[snorvich]

A whitish layer on a clownfish is almost always Brooklynella.
This fish needs immediate treatment (see below).

Here are a few articles about Brooklynella:
1. Brooklynella hostilis and Uronema marinum
2. http://www.chucksaddiction.com/brookynella.html
3. Identifying Parasitic Diseases in Marine Aquarium Fish - A Hobbyist's Guide to Identifying Some Common Marine Aquarium Parasites

The most effective treatment I found are formalin dips. Often one dip and afterwards transfer to a clean tank is enough to safe fish with early to clearly visible stages but if you want to make sure it is completely gone do dips every 3 days for 2 weeks, ideally done in combination with TTM to prevent reinfection (see 3. article).

For dips add 20 drops of formalin 37% to a gallon of saltwater (can be from the tank the fish is in), add an airstone or a small pump and then put the fish into this for 30 to 45 minutes (less if the fish shows signs of serious distress).
After the dip the fish needs to go into an uninfected (quarantine or hospital) tank.

This. The brook appears to be fairly advanced so time is of the essence.