Help identify brown plaque

[agorkov]

A brown bloom has appeared on the rocks in the aquarium. At first I thought they were dinoflagellates, but I couldn't find them under the microscope. Now there are two versions left: that these are some kind of unusual cyanobacteria or Chlorophyta. The bloom was significantly reduced after using Chemiclean, but then quickly returned. What have I encountered and how to deal with it?

 

[Ludders]

is there movement?

 

[agorkov]

is there movement?

No, they are motionless.

 

[taricha]

Signs of chrysophytes:

blobby gelatinous mucus
sometimes mucus so strong it holds shape out of water
light brown/tan/gold
under microscope, embedded in thick mucus
cells spaced out in the embedded mucus
cells are super tiny
cells nearly spherical
cells totally motionless

looks like you check 7 of the 8 boxes, (maybe not number 2)
pretty certain it's Chrysophytes