it is cyano ... cooper band butterfly if you can get one that lives there are also some crabs and snails that can help. make sure you have good water flow in the area as I have heard it is helpful in control of cyano. I had it in my 300 gal for a bit and let it get out of hand before I did anything about it. make sure your using zero tds rodi water and do frequent water changes with good quality water and it will go away over a few months
