The algae most likely is being fed by the excess food. Most people feed most once a day even skipping a day with no ill effects to the fish. In addition, the tap water is also fueling it as well. My first tank I started with tap water and had nothing but problems and it took months of using all ro
water to clear up my problems.
Also, flake food is notorious for having phosphates in it and can also be contributing to it as well.