Huge white spot on my Strawberry Basslet

Hi,

I picked up a Strawberry Basslet about a week ago. he was doing fine for a few days then, the past two days hes been hiding in this hole all day and night, but would comes out when foods around... then i noticed this!

Anyone know what it is? i don't think its ich because its too big...

I have him in a 10 gallon QT right now. But i don't know how to treat him.

 

Welcome to 3reef.

Really hard to tell from the images.

Just speculation it looks like it could be an injury caused from a laceration from the rock work.

Marine Fish Diseases and Parasites

Since I really can not tell what the malady is I would treat for bacterial first, just speculation again though.

If you go to the end of this link it provides common medication treats for the most common fish diseases.

Since you have him in a QT,

 

Unfortunately, the little was dead this morning.

I treated him one dose for furan-2 last night.
It does kind of look like he was hurt from my rocks or maybe another fish?
My stock is: firefish, flame angel, 4 line wrasse, 2 false percula clownfish and a few small hermit crabs. I never saw any fights between anyone...