That amount of light is above average. You will usually get algae problems with a new tank because it takes a while for the plants to become established and start taking up the nutrient. What you have is strong light and no nutrient take up. Patience grasshopper--use less light and wait until the plants get established, and do bigger water changes more often. Top ups don't help as they don't remove any nutrient. Don't add any ferts and remove the nutrient with water changes.