suface film and plant dips

Hey folks,
		I have a rack four 15g tanks which I use to experiment 
with various Plants and substrate systems.  In one I have C. wenditii and 
C. Baslli  (sp?) potted in terra cota (sp? again) trays with topsoil and 
vermiculite ala Kelly.  I also have some Java fern and willow moss 
attached to rocks and drifwood.  Inhabitants are 3 juvenille Kribensis, 
and SAE and an oto and a cory.  I'm getting that translucent white film 
on the top of the water. I've had it before and skimming the top over a 
period of time seems to eradicate it.  I remember it being talked about 
before but forget what was the collective wisdom.  As I recall some 
thought it was a bacteria some thought it was due to an iron surplus.  I 
change 20% of the water weekly and the tank is far from  over stocked.  
Filtration is by tetra phase II sponge filter driven by aquaclear 201 
Secondly, I'm familiar with 5% bleach solution to eradicate snail eggs 
and  algae on new plants.  Isn't there also a procedure using potassium  
permanganate (sp? yet again)??  Where does one get this stuff and how 
much does one use?
			Thank you all for your help.

					Miles Morrissey
					Easthampton, MA  USA
					mmorriss at sophia_smith.edu