I can see black brush algae on several leaves, but the long stringy algae could be Spirogyra. Doesn't really matter as like all "problem" algae, these two are caused by the same thing and can be dealt with the same way. In a planted tank, problem algae occurs when the light/nutrient balance is not "in balance." And we correct it by restoring the balance.
Light involves intensity, spectrum and duration because higher plants (unlike algae) are more particular. Nutrients required by the plants (there are 17) must be in sufficient levels to provide what the plants need to use the light, but not more. There is a narrow margin or leeway here, but it is limited.
To the fertilizer, if it is this one [
https://www.aquariumcoop.com/products/easy-green-all-in-one-fertilizer] it does not seem too bad, but it does have nitrogen and phosphorus, and neither of these should be added to an aquarium unless it is a high-tech method planted tank with intense light and diffused CO2. I will assume your tank is not, please correct me if I've assumed wrongly, but is like most of us a natural or low-tech method planted tank where fish are priority and plants are aesthetic and helpful in water conditioning. The six hours of LED suggest this method.
Six hours of tank lighting is not too much, so this would incline me to consider the nutrients as the issue. There may be too much of some...as I said, nitrogen is never needed in low-tech tanks because the fish plus the decomposition of organics primarily in the substrate will provide all the ammonia/ammonium the plants will need, and aquatic plants prefer nitrogen as ammonium, not nitrate. There is even some evidence that they will take up nitrite before nitrate. Reason is that nitrate (or nitrite) has to be changed back into ammonium in order for the plants to use it for this and that, and this take too much energy so it is a last resort so to speak. Phosphorus will be more than sufficient from fish foods. Both these additives can cause algae issues.
Do you have the nitrate level? And what is the GH and pH? The GH is important because it is a major source of calcium, and this nutrient is not included in the Easy Green.
