Persistent brown growth 5 months

[gurcuyo]

Hi all. I've had a brown algae growth in my tank for over a month now and I can't pin down what it is. On the glass it comes off easily with a magnet cleaner. There are no trapped bubbles and no slime or stringiness to it.

The tank is a skimmerless Waterbox AIO 25 that started from dry rock and has been running about 4 months. All key parameters are stable, with nitrates constantly below 20 ppm. I'd been rinsing my filter sock in tap water, so I stopped that two weeks ago, suspecting that might have caused the algae bloom.

Would appreciate help with identifying the algae type and any suggestions on how to deal with it.

 

[Mr. Mojo Rising]

"nitrates constantly below 20ppm".... to me thats high.
Do you perform regular water changes?
I don't see a powerhead on that glass, do you have any powerheads in the tank?

 

[gurcuyo]

"nitrates constantly below 20ppm".... to me thats high.
Do you perform regular water changes?
I don't see a powerhead on that glass, do you have any powerheads in the tank?

Thanks for looking!

I do 20% water changes every two weeks.

I am using the AIO waterbox Hidom AP-1500 return at 264 gph (single nozzle), no other powerhead beyond that.

Attaching a few other images for a full view of the tank