Bio-indicator = Brown Algae

Hiya Tom,

In one of my tanks I seem to have a lot of brown algae -- it is similar to BGA, but brown in color (grows in sheets, sticks to things but comes off with your thumb).

What is usually the cause of this?

Tank specs:

10g
110w of PC suspended over four 10g that are side-by-side (not end-to-end), so who knows? Maybe 30w of PC??
PH - this has fluctuated a LOT. I've had trouble getting consistency in distributing one CO2 canister to 4 tanks. It has been very high and very low.
Ferts - EI (dashes of phosphates, nitrates, potassium, and TMG)
It has no substrate and no fish.
Plants: Anubias (tons of it), a little bolbitis, and java ferns. I just recently added java moss in the hopes that it would use some of the nutrients since the other slow-growers may not have enough of an uptake.

The 10g that is adjacent to it with similar specs has NO brown bio-indicators. The only difference is that it's mostly java moss. Also no substrate or fish.

Kevmo!