Our pond was a mess. Chemicals didn’t seem to work. So I did a massive(for me) cleaning. Cleaned the filter, pumped out most of the water, filled it back up and used some Sheer Clear and some barley extract. UV light seems to be working. It was all for naught.
Few days later my wife got some sea salt(non-iodine) and dumped some in and the pond cleared up! We’ve always used salt, but had got out of the habit. Not sure that this will work for anyone else, but worked this time for us.