Great looking pond you have. I love the sealing wax palms and heliconias surrounding it, wish I could have the area around my pool stay looking like that but it only does for about half the year when it's warm here in Texas.
Regarding your algae problem, I'm not sure if anyone mentioned this amidst the pleco talk but something to consider that would not only look amazingly cool but also be fairly affective is flagtail prochilodus or fei feng as some know them. They eat algae fairly well and a shoal of them would be breath taking. 1 large triploid grass carp might work also if they are legal there and attainable. Also if you were still having black worm issues in the water or snail issues of any kind that you didn't want you could probably get by with some cupramine or similar copper additive as long as you didn't plan on intentionally keeping invertebrates in the pond in the future. It would wipe them out with a quickness. Although I must admit a shoal of clown loaches would be incredible and also easily decimate your snail population