Most of it is in this corner, all over this artificial rock/plant and on the natural rocks around it

Here you can see it on the output, and on the glass there's a big chunk that's hard to see behind the LED strip in the corner. That's a spot doesn't get scrubbed during cleaning because I'd have to remove the light diffuser and move the output.

these dark spots on this fake plant have been here forever, I don't think it's the same stuff...

here it's on the silicone/glass in the bottom corner... the captain disapproves.

I also have a healthy Pothos growing fast and happy in my aquaponic setup

The output on the aquaponic box leaves a reddish splash residoodoo on stuff, but I think that's just from the iron in my tap water.

Here's the setup in it's entirety

I try to do 50-80% water changes weekly, but more often than not it's every other week. I did one a week ago, and I'll probably do another today. I clean my filter media monthly.
I did a water test this morning, Ammonia/Nitrites @ zero, Nitrates 10-20ppm (seriously... the color difference on the API test kit is entirely indistinguishable
I don't have an airstone, the only oxygenating I achieve is through the output in the corner (which is significantly powerful, as you can see in the picture) and the output of the aquaponics (which is a slow trickle)
From what I've read about 'brown algae' it's typically diatoms, not algae... but its growing where there is plenty of current. I have an FX5 on a 40gallon... this water moves.
Other than scrubbing and water changes... what do I need to do to get rid of this stuff or keep it from spreading? I'm sure it isn't detrimental to the health of my animals, but it's ugly

