If you can add a container such as a plastic tub with an overflow, you could make a 'vegetable filter' and really harness the power of the cress!

Blanketweed enjoys the high oxygen content of moving water and does really well on water features and especially lovely sunny waterfalls. Oddly enough, if you had the same feature beneath an indoor aquarium it's known as an 'algae scrubber' and used for the removal of nitrates and phosphates

What algae really thrive on is tapwater - areas of the country with old victorian plumbing have phosphate added to prevent any lead dissolving and often nitrates are present too. This hard, alkaline highly oxygenated water is perfect for both green water and blanket weed growth. Then if you add the nutrient inputs of fish you can see that it's practically inevitable!