Active ingredient is malachite green, which contrary to popular belief does not have copper in it. It is totally organic. It gets it's name not because it's made of malachite, which has copper in it, but because the color of malachite green is close to the color of malachite and malachite green was often used as a cloth dye.
That said, malachite green is nasty to inverts even without copper in it.
That is something I've seen debated, with no clear winner, time and time again, and I've wrestled with that in my own mind ever since I started in the hobby when I was a kid. I always counted all catfish as scaleless just to be safe, as well as loaches and small tetras. With access to more and more customer support on websites these days, you could probably contact the manufacturer and they would probably give you their definition of "scaleless". You know, it's funny how sometimes you don't think of things like that when you're the one with the question, because I've never thought of contacting customer support before, lol.
WYite