If it were me I'd knock that stuff back before it get worse. Not sure exactly what it is from the picture, but fairly certain a product called Clipper would do the job on it.

It looks like a nutrient rich water condition. How long have you been running aeration to the pond? After the treatment to kill that stuff off, waters will be more nutrient rich. The next thing to do is consider adding some beneficial bacteria to compete for those nutrients. There are many brands that fall under the description of 'muck eating bacteria' that would help. Keeping the aeration going as much as possible will definitely help. Unless daytime temperatures are in going to exceed the mid 80s I'd let the air run 24 hours a day.