Coral suddenly turns brown and white hair like string strings came out

[Bennie_Oo]

Hello friends

my tank is approximately 1years and 2 months. Everything looks ok and happy. Last 3 days, most coral closed up and became brown. Some coral are seeing some white stringy things coming out of the flash. It is not the mucus for sure.

I am a real beginner for this hobby. please could you help what could be the possible cause based on your expertise? Thanks a lot and plz help.

 

[blaxsun]

First thing I'd check are all your tank parameters (salinity, temperature, etc.)