Whenever I top off my tank with well water for makeup water, I get a little bloom of brown along the rocks.
However if I top with RO
water, I get no bloom, therefore I am thinking there are silicates and stuff in my water. I don't know if you are using RO
water to top/change with or not?
If you're getting it on the substrate you can "storm" the substrate a bit with a turkey baster while you continue to add RO
water for changes and topoffs, see if that helps, storm it and let the filters clear water, repeat as needed.
Also - red legged hermit crabs do a nice job of controlling the brown algae if it is actually turning into brown hair algae, not so much the brown dusting.
Also a Lawnmower blenny will bite the brown diatoms/algae off of ANYthing, rocks, CC
, glass, sand, you name it.
So maybe a combination of thse things will help you out a bit. Also hihger nitrates in the water will encourage algae growth so if you feel like you might be overfeeding a bit then try dropping the feed back a notch
Oh and also adding kalkwasser to your makeup water is supposed to discourage growth of algae. I havent tried it yet.