Is this green Cyano

[Breadbox]

So I have this flat green film that hitch hiked from a coral frag, initially it spread slowly on one of the rocks but ever since I had the bright idea to give it a blow with my coral feeder a few weeks ago, it has being spreading like wildfire on the sand.

It is green under white light but brown under blue, does anyone have any idea what is it and what I do with it?

Needless to say, none of my clean up crew eats it, my urchin and abalone died mysteriously without ever taking a bite out of this

 

[Timfish]

Could be, I would carefully siphon it out. Any sand you siphon out can be soaked in H2O2 for a day or so, rinsed well in feresh water and returned to your system. Here's how I would do it