Fish dying suddenly, please help!

I have had my 75 gallon FOWLR set up for almost 4 years. I only use RO water, run a skimmer, and do a 15 gallon water change ever week. Around 2 months ago, I started getting a bad outbreak of hair algae. Water tested fine, but phosphates were a little high. Changed the canisters in my RO filter, and the phosphates came down, but the hair algae persisted. Started changing the water more often (every 5 days or so).
This week, I have lost 2 fish.
3 inch yellow tang that was the first fish I put in the tank almost 4 years ago, and a double saddle butterfly that was about 2 years old. Both of these guys were eating well and happy, seeming to die suddenly. They were eating flake, pellet, nori, and occasional cyclopeeze.
The two remaining fish are a maroon clown that is around 1 year old, and a picasso trigger that was added 3 months ago. These two are not looking good now. Their skin has white dots everywhere, and looks like it is starting to peel off (see picture of clown below).
It looks like ich to me, but I can't imagine that would be possible, seeing as the last fish was added 3 months ago, after a month of quarantine, and all of them were perfectly fine until this week.
Tested the water today, and things seem within normal range, although nitrates are a little high. Here are the results:
PH- 8.2
Ammonia- 0
Nitrate- 15
Nitrite- 0
Phosphates- 0
Can anyone help me figure out what's going on here?!?!?
 
It looks like brooklynella to me. However, this happened to the two fish that have already died this week, and to my understanding, brooklynella really only effects clowns.
 

swfishy

Administrator
Staff member
It appears to be Brooklynella. Brooklynella will affect any fish that it encounters.
Originally Brooklynella was called clownfish disease, however it was soon discovered that this parasite will attack any fish.
The treatment is generally formalin (I believe Beth covers this in her threads)
 
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