Why would you put leaves in your aquarium?

Adding dried Oak, Kapata (Indian Almond) and a few other species of safe leaves can  have the resulting effect of releasing humic substances, and this will lower the pH of the aquarium water, act as an anti-bacterial and anti-fungal agent, and also lower the heavy metal content of the water. It is widely accepted that it acts as a spawning trigger and can aid in the recovery of any fish damaged through stress or fighting. From my own observations and with the backing of some scientific research by the likes of Dr. Christian Steinberg, it has been proven that there are many positive reasons why using humic substance releasers, such as dead leaves, are good for the aquarium fish we keep.   At Finatics we offer Oak and Indian Almond leaves for sale for aquarium use. Here is a great article from TFH magazine on using dead Leaves in the aquarium:

http://www.tfhmagazine.com/details/articles/leaves-for-aquaria-full-article.htm