Can you send a picture?
Does it grow into long tendrils that flow around with the water?
It may be cyanobacteria. If so, it's a normal phase for a new tank to go through. You can pull it out as it grows. As you do, you're removing the nutrients that sustain it. It should eventually subside.
Mine went through this. I would pull out handfulls of it and it would grow back. After a month or so, it just disappeared. I'm not certain if the purigen or carbon I added helped. This was in my 12 gallon
jbj nano.