As mentioned, you have what sounds like blanketn weed. A UV, shade or anything else will not prevent it. UV will help clear green water but not BW.
There is some stuff on the market which is available at most aquatic/pond shops and it's called "Cloverleaf blanket answer" It's about �17 for a bottle and it's like flour....you mix it with water and sprinkle it the pond. It's not a chemical, it's an enzyme which works by puncturing the single cell algea (blanket weed is made up of single celled algea) and the blanket weed literally "leaks" to death.
I use this stuff on my koi pond......i used it 3 years ago and ive not had a single bit of BW since although other ponds may vary and it is recommended to dose 8 times a year !!!!!
It's well worth the money.
Good luck