One tactic I've had great success with has been to do large water changes (at least 25% per week). This way you're not introducing unneeded chemicals into your pond. You're actually helping the fish, while you're controlling the unwanted algae in your pond. Wet Pets in Georgia put me on to this algae-controlling trick years ago. Chuck Jones (owner of Wet Pets) and his staff have to be some of the most knowledgeable people out there when it comes to koi ponds and their upkeep.
I was skeptical about this tactic at first, but it has really worked well for me. The large water changes tend to starve the algae for nutrients. When you do large water changes like that, you're removing large quantities of nitrates (the plant food algae feeds on).
Unfortunately, there's a lot of mendacious information about algae control out there. I've tried a lot of these ideas over the years and have found few of them to be effective.
By the way, I hope you have a dedicated water meter for your pond. If you don't, doing water changes in a pond that size can be very expensive. On a pond your size, it's almost a requirement.
Now you know I'm gonna want to see some picks of your pond. No hurry. Whenever it's convenient. Take care.