Wow, I have been reefing for 20 years and I don't know what that is or how to get rid of it. You could try removing a rock it's on and hitting it with a strong kalkwasser paste and see if that burns it. Then rinse the rock off with saltwater before placing back in the tank.
Looks like a sponge with brown algae growing in top. If si0o it should pull off essily and be easy to mash. It's possibly feeding off DOC in your system. Regardless I'd review everything that's happened or changed in the last 5 or 6 months to figure out why it's doing so well.
Thank you all for your responses. It is very soft and it tends to float and then get caught in powerheads / overflow. I will take the suggestions of trying to siphon it out and remove what i can see but the issue is it keeps coming back and is very aggressive and on all rocks and will grow on the glass and overflows as well.