Brown things under Goniapora

[iArady]

Hello ,
I have spotted these little brown algea like things under my coral . I dont know what is this and i dont have anything like this in my other goniapora
What should i do ? Is it sick?
i cleaned some of these things with pipette and it seems okay for now .

Tank age : 6month
Ca : 450
Mg : 1300
Phosphate : 0/01
Nitrate : 3ppm
Kh : 8/6

 

[blaxsun]

It kind of looks like a small leather coral - or possibly a xenia. Not 100%, sorry.