Looks like green cyano. Couple of questions
Do you have CUC present? If not I would start to increase the amount of CUC you have
What are your parameters? I would make sure those are all stable and not too high or low
If you can, I would try and syphon as much of it as you can, do it during water changes as this can make it easier (at least it does to me, haha)
Others will be able to give you more suggestions on how to get rid of it!