Hi mbty
True brown filamentous alga?
The reflex might be to think
Sphacelaria, but a ton of browns have a filamentous, gamete-producing (sexual) stage ---in tandem with a macro, spore-bearing stage. That stuff could be anything.
My best guess for its sudden dominance is that the tank revamp pretty much wiped the slate clean of other algae, but that spores of the browns remained in the rock.
...but then you're saying there's nothing in the tanks at all.
If you mean nothing but water, then there's the chance that either the water or the saltmix (if it's even possible), or the probes, rags, implements, or buckets bore contamination with JUST the brown kind of spores.
In such a water-only scenario, and assuming all manner of spores (greens and reds too) are present. I don't know of any chemical limiting factor that would discriminate so heavily in favor of the browns.
But heck, I don't know 2% of what there is to know, and maybe somebody has the inside on this.
horge
