Yellow Tail Blue Damsel looking sick

[Notathumpa]

Hi. I have 5 Yellow Tail Blue Damsels in my reef tank. Have had them for a couple of months and all have been well. The largest of them has suddenly developed dark blotches on the body and appears sickly since yesterday. Any ideas on diagnosis or action I should take?

 

[Notathumpa]

1. How old is this aquarium? 5 months

2. If less than six months old, what is ammonia level? Not tested

3. What is SG of this aquarium? How measured? 1.026 by refractometer

4. When was the last fish added to this aquarium? 2 days ago. No signs of ilness.

5. Was it quarantined? NO If so, how? And how long? Was it prophylactically treated? How?

6. If you are using a copper based medication, which one? How often do you measure level? When?

7. If you are using hyposalinity, how did you calibrate your refractometer?

8. Please describe in detail, the appearance of the fish? If there is one or more pimples, are they lumpy? What color? Has dark blotches on body on both sides of fish.

9. Please describe the behavior of the fish as best you can. Is it acting reclusive? Is it always up towards the top of the aquarium? Is it avoiding light? How active is the fish?
Was out with others this morning but is hiding now.
10. Is the fish eating? What? Would not attempt to eat, but ate fine last night. Frozen mix of meaty foods and pellets.

 

[jmm]

Whenever I had that many yellow-tailed blue damsels in a tank they killed each other off one by one until only one or two remained.

 

[Notathumpa]

Thanks, jmm. Damsels were well behaved. Lost two and a Royal Gramma plus a KoleTang about a week ago. I think the Kole brought something in from the LFS which is where the Gramma and some of the five Damsels came from as well. Makes me suspicious. So far the remaining fish in my tank (not from same lfs) look OK. I might give a treatment to the whole tank since it's still new and light on bioload. Looking at PraziPro followed up with API PIMAFIX.