Well, I'm not an expert, but I can tell you this - those are both signs of an excess of nutrients in your pond. Foam means phosphates are high so you probably have an excess of organic material decomposing in the pond. But remember that these are both symptoms - they are not problems in and of themselves. Identify and address the cause and the symptoms will disappear.
More information would be helpful - how big is the pond? How old? What kind of filtration?