Fish only tank with live rock problem

[hammadkatiyar]

I have fowlr tank more than 3 years. Last three months, I didn't add any fish. Two weeks back, I added flame angel. She was eating well initially but suddenly she died after 2 weeks. I checked my water parameters, they were fine n moreover my old fish which was in this tank for last one year, she also died yesterday. I didn't see any fish fight. What could be the reason?

 

[Daniel62]

marine velvet maybe

 

[ebushrow]

Certain fish are very sensitive to high nitrate levels, I am not sure if that is the issue here, however, are you doing regular water changes? This of course may not be a/the cause, however its a place to start.