I have used 2 products for the black algae on roofs and general cleaning on the house, 30 seconds and wet and forget. I have also made my own cleaner if i didn't feel like going to the store. The Wet and Forget feels like its a little more potent to me. That's why I started using 30 seconds and have been happy with it. Seems to not be so harsh and doing what i do on the majority of the house annually you dont need to use as much or as harsh of a chemical. I have used 1 cup of trisodium phosphate, 1 gallon of bleach and between 3 and 5 gallons of water and make your own as well and apply with a pump sprayer and rinse off. On my roof i usually wet everything well with the hose and apply the cleaner stronger than recommened and let set for 10-15 minutes and risne off.
