strange film

I have a strange film on the surface of the water. It seems to have just started since i started adding some chemicals, i.e. Reef Plus, stronium, iodine and calcium. Is this normal and is this the cause?
55 gal
CPR back pack skimmer
Fluval 204
2 Maxijet 500 (500 gal per hr)
50 or so punds of live fiji
crushed coral rock
Light is 2 48" 40 watt Actinic and 2 10,000K 48" full Spectrum
LIFE:
2 Yellow tangs
2 Clowns
1 red Firehawk
1 Condy
4 snails
3 hermit crabs
 
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