It looks like a form of cyanobactor to me.....PM Bill Cody and see about sending him a sample to identify....Bill, I believe, can also suggest a treatment or chemical your algal species is sensitive to.
Some of the WORST things done in a pond are just blindly "throwing" things at an issue.....Ponds are in constant change, but one mistake can cause unintended consequences that take years and truck loads of money to fix....
