Improper filtration and seasonal algae bloom can create a film on the surface of a fish pond. By draining at least two thirds of the existing water and adding fresh water along with cleaning your filter to aid in increased circulation should clear up the surface film in a few days.
Simply run the water over the surface level for 10 - 15 minutes a couple of times a week to keep the surface clear. Remember to use dechlorinator each time.
Having a circulating filter helps. If you don't have a filter you could try using a spoon and just barely push it down under the surface of the water to skime the film off. Another trick is to use paper towels and gently drag it across the top.
A difficult but permanent solution would be to clean the fish pond thoroughly, by draining all the current water out, scrubbing the pond walls, and refilling with fresh clean water.
