Red Slime on right side of tank?

[JCOLE]

Over the past couple of weeks I have developed a red slime on my sand bed. It is on the right side only which is weird. The only think different on the right side is a HOB protein skimmer. It has been there for 5 months though. Everything else is uniform.

Any ideas? Also, what is it and how do I get rid of it?

Thank you

 

[Jason mack]

Yes , that’s cynobacteria ... I would try to syphon as much out as possible , and try and add more flow too that area , you also want too add some bacteria too ..!