Dosing potassium with banana?

[David Marshburn <marshbur at cs_unc.edu>]

It's wild-hair night tonight at Howell Park, and I'm considering
introducing potassium into the tank by feeding banana pieces to 
the bottom-dwellers (or trying to...).  Suggestions of feeding 
peeled peas or blanched zucchini to the bottom-dwellers and algae-
eaters, along with claims by the USDA that bananas are a good 
source of potassium, have inspired this thought. Before I go and 
do anything rash, though, I thought I might inquire if wiser heads 
knew of any reason that this might poison the tank (as long as any 
uneaten banana were removed before it decays).

In a related question, where does all the potassium that plants use 
in the wild come from?  Certainly, it's "naturally occurring", but 
what's the source?  (I suppose I should go find a freshwater ecology
book, huh? :)

cheers,
-David