I'm not sure. Its by accident I even have it. I was looking for a low tech carpeting plant and happened to see it advertised on a shady website. I said "heck with it", it's only money if it never arrives. Sure enough, it arrived and now that site has been taken down. There's not too much information, that I can find, about it.
There's some interesting research going on about cold tanks with soft water growing plants that require CO2, yet no additional CO2 is being used. Might be why you are having success with it. I wouldn't believe it without seeing your picture. Amazing work!
What's the pH of this tank?