There is a post in here about doc, dissolved organic compounds, that may be what is happening. It is dirt oil etc that is dissolved in the water, makes it foam a little.
Some have built an foam filter.
I don't think it hurts anything having the bubbles, but wait for the koi keepers to let you know their opinion.
thanks addy, i don't think it is anything to do with dirt oil etc unless it has come from the new food i have just started to use. There has been no other changes made to the pond in the last 2 weeks.
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