If you are using the light that came with your hood, and the greenish algae is hard to scrap off the tank then you are better off buying a new light than buying a tank mate. You can get shrimp or a snail for the green algae if you want, but the brown algae won't be eaten.
The box and bulb will have the Kelvin rating listed. I use Zoo Med Flora Sun
for low light plants and Zoo Med Ultra Sun
is available for high light plants. Those lights have the Kelvin and type of light displayed on the box. You can also get Flourescent bulbs from Walmart for cheap. I'm not sure which type of light to suggest until I know what your plants need. There's no point to blasting your tank with 6500K if your plants only need 5500K. :) Do you know what type of light your plants need? If not do you know their names?