Hey Ira,

Thank you for your question! On My Land Plan we have some tips for how to care for ponds more generally that can help your pond. For the buildup of Green algae specifically here are a few tips:

Barley Straw especially can help discourage some algae buildup.

Introducing water snails or tadpoles can also help, as these scavengers can reduce algae levels. If it's floating, using a pole to remove the algae manually can also remove some of this.

In the future, ensuring that only low nutrient aquatic plants are present or potentially installing a filter in the pond can help reduce levels.

The royal horticultural society offers some more tips.

Best,
Dan Hubbell
Feel free to email us at info@mylandplan.org if you have any other questions!