I have never used CO2 and I have had java moss take over tanks. It took over my 10g with very little light and adhered to nothing. It's now adhered itself to the glass in a few places and gets direct sunlight part of the day. It really seems like so long as it doesn't get moved around it doesn't matter if it's attached to something. I forgot about a 1.5g that had some java moss in it, sat in a closet for 6 months and was really gross.. I rinsed everything and stuck it on a desk and it started growing almost instantly. It just floats it the middle.
There's a clump my electric cat is always jostling around that grows very very slowly. It stuck to some wood at one point and took off but he tore it of and it seems like it almost stopped growing.
I removed most of it from my other tanks this summer because I didn't have time to keep trimming it. I was throwing a few pounds of it away every 2 weeks!
Now I have 5 tanks that get a lot of direct and indireect sun, 2 brackish 3 fresh, the only one that grows algea bad enough that I have to scrape at least once a month is RIGHT next to the window and was badly overstocked until recently. I'm adding more plants soon (possibly java moss) and I expect that will take care of the algea.
