Help identify??

[steelermags]

Tank is 125G reef tank in which I use RO/DO water and do water changes once a week. Tank has been up and running for 7 months. I have several fish, polyps, and anemones. Recently this red film showed up on my sand and some rocks. Can you help identify as well as where and how it came about? all feedback is appreciated.

Steelermags

 

[SeahorseKeeper]

It looks like cyano mixed with coralline and this comes from excess nutrients, lack of flow and sometimes occurs when the bulbs need changing. What are your parameters?