What I am basing the thoughts of Dino on is the first photo you posted.
In the upper right hand corner of the photo the rock comes from the side of the photo and curves up.
After a bit it makes a sharper climb toward the top of the photo. Just to the right of where the rock sharply curves up there appears to be bubbles attached to stringy appendages of the red stuff. Is this correct?
If it is dino you may just need to raise your phosphate a little.
The phosphate will allow the algae to out compete the Dino.
So I would remove any phosphate control you have, leave in any nitrate reduction that you want to.
If the phosphate gets too high then you can judiciously re-intoduce phosphate control.