Yellowing leaves, weak stems, and algae killing plant leaves. What should I dose?

[Tech Support KM]

Hi there, thanks for reaching out!

Can you tell me if you are currently dosing any supplements to the tank?

[ryan.lippy]

So I have had planted tanks in the past with no problem but I have only had headaches with my current tank. Its a 20 gallon with parameters as follows (PH ~ 7, Ammonia - 0, Nitrite- 0, Nitrate <5, Temp: 78 degrees).
As of now I have problems with filamentous algae and slimy green algae that grows on plants and kills leaves. I also notice that over time lots of my leaves become a yellowish color and that the stems soften up and break. I think I have a macro nutrient problem in the aquarium. From these symptoms what should I dose in my aquarium to try and help remedy the problem, and what can I do to get rid of the existing algae? Ive tried to remove algae manually but it is near impossible to get off plants.