Film on fish-tank water and ammonia swing?

I have a filtered and heated 10 gallon aquarium which houses a betta one side of the divider and a dwarf puffer on the other.

Yesterday I did a 25% water change, and today the betta's side of the tank has a film on top of the water, and the tank is more cloudy.
The ammonia level is around .5, and it was around .3 yesterday BEFORE the water change.

I added the correct amount of water conditioner and the PH stabilizer.
What is going on!?
 
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