I've been using k-leaves since day one. k-leaves release several weak organic acids like humic and tannins which lower the pH of the water; and also explains why it gives the weak-tea like coloration...
Just do a simple search in the internet and you can get tons of information on this.
http://www.siamsbestbettas.com/articles.html
Alternatively, you can buy this off the shelves of most LFS...
hope this helps.