@dieselplower @mariobrothersleeve Children children please !!!!.....
Algae is a plant and like a plant it takes in co2 during the day giving us oxygen , at night like any other plant it goes into reverse.
To much in the way of nutrients can cause algae to bloom , my pond is covered sides and bottom with a thin covering of algae, thankfully I dont have a problem with string algae and never have had.
I put this down to regulasr maintence of the pond and its systems .
Potasium Permanganate can be used to kill it but your also nuking the rest of your system so extra airstones should be added .
Do you have a phosphate test kit MBS if so whats your reading please , also how many times do you do a water change in a year you should be doing partial ones on a regular basis.
What about filter maintenance we do ours three times a year late spring, late summer and Autumn , when was the last time you chenged your UVC it all goes to help
Dave