Hi Banditpowercoat and Leah.
Thanks for your help.
I think you are right it was the LR that caused this outbreak (I remember before all mess, I heavily fed the tank but there were not signs of cyano). Thanks to Red Coral, I got some chaeto today. I put this in the back of the tank. I also did 20% water change today and sucked the cyano out. I also rearranged some rocks which I suspected there are dead spots. Again, at the end of the day after water change, I noticed bubbles appear on the rock again
.
I will definitely try your way (complete light out) in a week or so when things don't improve.
Thanks