Did I read that you have Ozone filters too Fred ?
What?? You mean my pond has an Ozone layer??
That should stop the UV making Algae!!
I used to keep a marine tank in the UK so I do have some understanding of water Chemistry how to convert Ammonia/ nitrites to nitrates which is then consumed by plants like lillies ect..

Those crates are full of plastic shreds and as the water runs over them the Good bacteria starts to colonize and its these that convert Ammonia and nitrite into nitrate..
I have heard that pond keepers occasionally "salt their ponds" and never really looked into it..
I will now so thank Graham.

is there going to be no shade at all in the pond ?because the algea will grow rapidly i think .A friend of mine built a pond in uk similar size to yours uncovered after 12 months the water was like pea soup lol and could,nt see his fish .so he put up a tarpulin and added a U.V light and the problem went away .
Yeah I know! Not full sun as we have tree shade but we are looking at different types of cheap tarp and fishing nets till the Talisay tree covers the whole pond..