There is always a bit of foam on the surface of my goldfish pond. I vacuum the bottom regularly. I promptly remove what little leaves and dead vegetation that get in it. Phosphate tests regularly show 0.0 to 0.25 ppm. All the other water chemistry is consistently stable within acceptable limits. The foam doesn't seem to do any harm. The 15 - 20 goldfish appear quite healthy.
Any ideas what is causing the foam?
Any ideas what is causing the foam?