With the amount of light you have you absolutely have to use CO2 if you don't want a BBA garden, which you now have. That tank and light fixture were designed for a reef tank, which takes a lot more light than a planted tank. Along with the CO2 you absolutely have to dose the water - nitrogen (nitrates), potassium, and phosporous (phosphates), plus trace elements, including iron, and a little magnesium unless your water naturally contains adequate magnesium.
"Green slime" algae is blue green "algae", actually a bacteria. It usually shows up when you have too much light and when you are short of nitrogen (nitrates).
One thing you can try is putting a layer of fiberglass window screen, sold as insect screen over the lights to reduce the intensity. Each layer will drop the intensity by about 40%. One or two layers will do it.
As bad as your BBA is now I think you should replace all of the plants, clean everything else in the tank very well to eliminate all of the living BBA, and start over with lower light and good fertilizing.