I would try to have all your hours at 50%, you could also try 6 hours for a while to see if it helps. Too much light is a very common cause of algae, especially when you also have it on the hardscape.My lights are currently on for 7 hours a day and 4h of that is at 50% intensity (1 bulb off).
Get a fertilizer containing nitrate and phosphate. Having a bit too much doesnt do much harm but letting your plants go hungry for something means they suffer and start releasing compounds that algae use as a signal to attack.