Zoas closed and slowly getting covered with brown layer

[artursm15]

Hello guys so i have some problem with my zoas some colonys/frags with zoas kinda slowly dies and some colony just looks great .. it kinda starts with first polyps closed then brown layer on top and then they just rot. Have tryd dipping in peroxide , manual removal the small layer , blasting with turkey buster ( or how you call it ) moveing to higher flow areas colonys/ frags with not big succes

My salinity 1.026
Mag 1300
Calc 400-420
Alk 8.2-9
Temp:27c

Using carbon , phosphate remover
Total system volume arround 350-400 liter
Doing 10-20% wc weekly !

 

[BlueMoods]

Are you dosing carbon and trace elements, like vodka and Purple Tech? If not give that a try, my zoas love it, never had one not open within 45 mins of being put in my tanks. (2 nano tanks going, both with 3 to 6 zoa colors in them.)