Well it's been while (about 2 months) since I bought any plants. Last ones were dwarf hair grass, which didn't really take off. I guess I need more lighting. I have only 2x14 watt T5 NO. And it's a 25 gal. My guess the java moss hitchhiked with my java fern, which I bought about 4 months ago. I see some more of the java moss near the roots of the java fern!