Oak leaves for shrimp tanks?

I soaked them for a couple of days but they float up in the filter flow, so I put a stone on them....
 
ooh this was something that i remember reading about too but i forgot about it, I only wish there were some trees around my area that I could be sure are pesticide-free. I will file this away for future reference though, thanks everyone.
 
AquariaCentral.com