Fixing green pond water is pretty easy once you understand the role bacteria plays in processing nutrients.

Here's some helpful links:

DIY filters-    • OZPOND DIY POND FILTER VIDEOS  

Helpful video for dealing with string algae -    • Get rid of algae in your pond Naturally!  

Pond aerator (amazon link)- https://amzn.to/3P9pJU3.

Solar aerator (amazon link)- https://amzn.to/3nWcvxZ

Pond flocculent (amazon link)- https://amzn.to/3RyMIcH
If you make a purchase i may receive a commission at no extra cost to you.

Diatomix- https://diatomix.com.au/?v=6cc98ba2045f. Use coupon code ozponds for free shipping.

If you don't live in Australia you could try nualgai- https://amzn.to/3gTrt4f (amazon link). It also promotes the growth of diatoms to outcompete problem algae.