what type of lighting are you using,are you dosing any ferts,and you need way more plants than that to out compete the algae.you need tons of stem and fast growing plants to start out with so the algae does not use up the nutrients before the plants are able to use them.try getting a fert plan together and using seachem excel.its great to help fend off algae although its not the cure all.you will need to get things stable first..remember way more fast growing plants,good lighting,and proper nutrients..most people think they can add a few live plants say 6 or 7 and think they have plenty.you need a great deal of the substrate covered in plants that grow fast till you work out a plan that is best for your tank,then you can slowly remove stems and add slower growing plants to your liking,a good substrate is crucial to healthy plant growth also.